Custom Integration vs iPaaS Cost: The Real Three-Year Comparison

The custom integration vs iPaaS cost question rarely gets an honest answer. Vendors on both sides quote Year 1 and stop there. This article models all three years for a typical mid-market ERP integration, prices in the two costs most quotes leave out, and shows clearly where custom code comes out ahead.

The short answer: for one standard ERP-to-eCommerce integration, the midpoint three-year cost is about 64,050 for custom middleware and about $46,880 for iPaaS. Add a developer departure or heavier API maintenance, and the custom figure rises to between $78,330 and 135,030. A small, stable custom build can still beat a premium iPaaS plan. A complex, frequently changing one almost never does.

What Each Approach Actually Means

Before comparing costs, it helps to define what is being compared.

Custom middleware is code a developer writes specifically for your business. It connects your systems exactly the way you want, handles your data formats, and lives in a repository your team owns. You control everything, and you maintain everything: hosting, monitoring, error handling, and every change when a connected system updates its API.

iPaaS (Integration Platform as a Service) is a managed platform with pre-built connectors for common business systems. You configure workflows instead of writing them from scratch. The vendor runs the infrastructure and typically updates connectors when a supported application changes its API.

The real difference is not features. It is who carries the ongoing cost of keeping the integration working.

The Assumptions Behind the Numbers

Most build vs buy comparisons hide their assumptions. Here are ours, so you can swap in your own figures.

• Scope: one integration between an ERP and an eCommerce platform, covering orders, inventory, customers, and pricing.
• Developer cost: a fully loaded US senior engineer at 175,000 per year, the low end of the 250,000 range in Truto's build vs buy TCO analysis. That works out to about 84 per hour across 2,080 working hours.
• Custom build effort: 300 to 700 hours, depending on mapping complexity and error handling (midpoint 500 hours).
• Custom baseline maintenance: 15% to 20% of the build cost every year.
• iPaaS setup: 5,000 to 15,000 for implementation and configuration.
• iPaaS subscription: 3,600 to 15,000 in Year 1, rising 5% at each renewal.
• iPaaS internal admin: 12 to 48 hours per year of your team’s time to monitor and adjust workflows.

These are planning assumptions for a typical mid-market scenario, not quotes. Your numbers will differ, and the method later in this article shows how to plug them in.

Custom Integration vs iPaaS Cost: The Three-Year Comparison

Most build vs buy comparisons only show Year 1. That is where custom code looks most competitive, because ongoing costs have not arrived yet. The picture changes by Year 3.

Year-by-year view (midpoint scenario)

Full range across scenarios

How to read the table:

• The ranges overlap. A low-complexity custom build ($36,540) costs less than a mid-priced or premium iPaaS plan. That is a real result, not a rounding error.
• The base case assumes nothing goes wrong. The rows below it show what happens when the two most common risks arrive.
• Custom figures exclude hosting, logging, and alerting infrastructure. iPaaS figures exclude per-transaction overage charges, which some vendors add at scale.

The Two Hidden Costs That Tip the Balance

The base case assumes a stable environment and the same developer for three years. In practice, two factors regularly push custom builds past their original budget.

Maintenance Drift

Maintenance drift is the gradual rise in the cost of keeping a custom integration working as the systems around it change. Your ERP releases updates. Your eCommerce platform, CRM, and shipping carrier each change their APIs on their own schedules. Any of these changes can break an integration that worked yesterday.

The baseline in our model, 15% to 20% of the build cost each year, matches the figure cited in Fullcast's software build vs buy analysis. For complex connectors, the real figure is often higher. Truto, an integration API vendor, estimates that maintaining a single connector consumes about 15% of one engineer's time, which it calls a conservative estimate. At a 175,000 fully loaded cost, that is 26,250 per year, more than three times our baseline midpoint.

That is the "maintenance drift" row in the table. If your ERP or storefront releases frequent API changes, plan closer to this line than to the base case.

On a managed iPaaS, the vendor typically absorbs connector updates for supported applications, so your maintenance cost stays inside the subscription.

Key-Person Risk (Developer Dependency)

Custom integrations are usually built by one or two developers who understand exactly how the code works. When one of them leaves, that knowledge often leaves with them. The integration does not stop on the day they resign. It stops the first time something breaks and nobody knows why.

We priced one departure in Year 2 at 120 to 220 hours of internal effort: 40 to 60 hours of hiring and interview time, plus 80 to 160 hours for a replacement to learn an unfamiliar codebase. At 84 per hour, that is $10,080 to 18,480. This excludes recruiter fees and the cost of any downtime while the integration is unsupported, so treat it as a floor.

This is how technical debt builds up. In a 2020 McKinsey survey of 50 CIOs at large financial-services and technology companies, respondents said 10% to 20% of the technology budget meant for new products is diverted to resolving tech-debt issues. Mid-market teams have smaller budgets, so the same diversion hurts more.

An iPaaS reduces this risk but does not remove it. Workflows are visual and documented on the platform, so a trained admin can read and adjust them. You still need at least two people who know the platform, not one.

The Hidden Costs on the iPaaS Side

A fair comparison has to name the costs that iPaaS quotes leave out too. Our model already includes two of them: internal admin time and renewal increases. Watch for these as well:

• Usage-based pricing. Some platforms charge per task, per execution, or per connection. At high order volumes, these charges can grow faster than your revenue.
• Premium connector fees. ERP and enterprise connectors are sometimes priced as add-ons, separate from the base plan.
• Implementation partner costs. If the vendor relies on partners for setup, the implementation fee may sit outside the subscription quote.
• Lock-in and exit cost. Moving off a platform means rebuilding workflows elsewhere. Ask how workflows and mappings can be exported before you sign.
• Renewal terms. First-year discounts often disappear at renewal. Ask for the Year 2 and Year 3 price in writing.

None of these make iPaaS the wrong choice. They make it a choice you should model with the same rigour as a custom build.

Where Custom Code Wins

Custom middleware is the right answer in specific situations. Saying so clearly matters, because a cost comparison that pretends iPaaS always wins is not useful to anyone.

Custom code makes more sense when:

• The integration is simple and will not change. Our low-end custom scenario ($36,540) beats every iPaaS scenario above the low end. If you have one stable flow between two systems that rarely update, maintenance stays low and the build cost is paid once.
• Your transaction volume is very high and your platform charges per task. At high volumes, usage-based fees can outgrow a flat-cost custom build. Calculate your monthly volume against your shortlisted vendor's pricing before you decide.
• Your business logic is truly unique. Proprietary validation rules, unusual data transformations, or logic no connector can express may need code. A capable iPaaS handles most standard mapping and conditional logic, but there are edge cases where it cannot.
• You already have a strong in-house integration team. If two or more engineers already maintain similar code, the key-person risk and the marginal maintenance cost are both lower.
• Your data must stay fully air-gapped. If data can never touch a third-party cloud, even for configuration, a self-hosted build may be the only option. Many requirements are less strict than this, though. Platforms that support hybrid deployment can process data inside your network through an on-premise agent. Our guide to on-premise vs cloud integration explains the trade-offs.

The honest summary: if your integration is simple and stable, your volumes are extreme, or your data rules are absolute, evaluate custom seriously. For most mid-market businesses connecting standard ERP, eCommerce, and CRM systems, those conditions do not apply.

How to Calculate Your Own Three-Year TCO

The tables above are a starting point. Use this four-step method to get a number that reflects your business.

• Get a fully loaded build quote. Ask for hours covering build, testing, documentation, and error handling. Multiply by your fully loaded hourly cost (salary plus benefits, payroll taxes, and overhead), not the base salary.
• Project maintenance at two levels. Model a baseline at 15% to 20% of the build cost per year, and a drift case at 15% of one senior engineer's annual cost. Use the drift case if any connected system releases API changes more than once or twice a year.
• Price one key-person event. Assume the main developer leaves once in three years. Add hiring time, ramp-up hours on the existing codebase, and an allowance for downtime.
• Get an iPaaS quote with the full picture. Include setup, all three years of subscription at renewal pricing, any per-transaction or premium connector fees, and your team’s admin hours.

Then compare the three-year totals side by side, under the same scenarios.

Rule of thumb: in our experience, if a pre-built connector covers 80% or more of your requirements, buying usually costs less over three years than building.

What This Means for ERP Integration

ERP integrations are one of the most common areas where businesses default to custom code. The ERP feels complex, so the assumption is that only a developer can handle it.

That assumption is increasingly outdated. ERP-focused integration platforms now offer pre-built connectors for SAP Business One, Microsoft Dynamics 365 Business Central, NetSuite, Sage, and other mid-market ERPs. These connectors come with the data mapping, error logging, and sync logic that would otherwise need custom code.

For a business connecting its ERP to Shopify, a pre-built connector can handle order import, inventory sync, customer records, and pricing in a fraction of the time a custom build takes, and the vendor manages updates when either platform changes its API.

APPSeCONNECT was built specifically for this use case, and it is the iPaaS core that powers appse ai's AI workflow automation platform. Its SAP Business One integrations and connectors for Dynamics 365 Business Central, NetSuite, and Sage cover the standard ERP-to-eCommerce and ERP-to-CRM flows most mid-market businesses need. Packaged ERP integrations start at 99 per month, with setup and ongoing management handled by the APPSeCONNECT team. See what is included in our guide to ERP integration for 99/month.

If your ERP integration falls into the standard category (orders, inventory, pricing, customer data), evaluate a pre-built connector before you commit to a custom build.

Want your own three-year numbers?

Talk our experts and share your ERP, your connected apps, and your monthly order volume, and our team will model custom vs iPaaS cost for your stack, including the drift and key-person scenarios above.

Frequently Asked Questions