How Much API Integration Costs in a Custom Web App (London, 2026)

The verdict in three sentences

A simple API integration (REST, one endpoint, read-only) costs 2,500 to 6,000 EUR in London in 2026, while a complex integration with two-way sync and error handling runs 8,000 to 20,000 EUR. A backend developer day rate ranges from 450 to 650 EUR, with delivery in 2 to 5 weeks depending on the number of endpoints. Below three connections and without heavy business logic, an iPaaS (Make, Zapier) at 20-99 EUR/month is enough; beyond that, a custom connector pays for itself within 18 months.

What really drives the price

Integration cost doesn't depend on the "number of APIs" but on the logic wrapped around them: field mapping, error handling, reconciliation, idempotency, logging. Here are the 2026 ranges for a London SME.

These figures assume a documented, stable target API. A poorly documented third-party API without a sandbox easily adds 20 to 40 % of effort.

Total 3-year cost: custom vs iPaaS

The CIO's real question isn't the project price but the total cost of ownership. An iPaaS bills by operation volume; a custom connector has an upfront cost then ongoing maintenance.

Custom costs more in absolute terms, but becomes relevant as soon as volume blows past iPaaS tiers or business logic exceeds what "no-code" handles cleanly (financial transactions, compliance, accounting reconciliation).

Mini case study

Julien, CIO of a 45-person SaaS SME in London, wants to connect his billing app to Stripe and to his accounting software. Chosen quote: 9,500 EUR for the two-way Stripe sync (payments, refunds, webhooks) and 4,500 EUR for the accounting export, totalling 14,000 EUR. Maintenance at 650 EUR/month. Today two people each spend 6 hrs/week re-keying payments, i.e. 12 hrs at a loaded cost of 40 EUR/hr = 480 EUR/week, ~20,800 EUR/year. The integration pays for itself in 10 months excluding reliability gains, and removes the reconciliation gaps that delayed monthly close.

FAQ

How much does a simple Stripe connection cost in 2026?

Expect 2,500 to 5,000 EUR for a checkout and payment webhook reception. Add 3,000 to 6,000 EUR if you handle refunds, subscriptions and accounting reconciliation.

Do I need to pay for maintenance after delivery?

Yes, maintenance of 400 to 900 EUR/month is recommended: third-party APIs change versions, deprecate endpoints and alter formats. Without it, a breaking change can halt your flows overnight.

iPaaS or custom: how do I decide?

Below 3 connections, with no heavy financial logic and low volumes, iPaaS at 20-99 EUR/month wins. Beyond that, or as soon as compliance demands it, a custom connector pays back in roughly 18 months.

What timeline should I plan for?

From 2-3 weeks for a simple endpoint to 6-9 weeks for a multi-API orchestration. The limiting factor is almost always documentation quality and access to a sandbox on the target API side.

What if the third-party API is poorly documented?

Plan for a reverse-engineering phase and 20 to 40 % extra effort. You de-risk the budget by adding a contingency and scoping a separately billed "discovery" work package.

Let's scope your project. Describe the APIs to connect, the volumes and the level of sync required: we'll price integration plus maintenance, a 2026 order of magnitude of 5,000 to 20,000 EUR. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.