The verdict in three sentences
A bidirectional API integration across CRM, ERP and billing costs, in 2026, from 8,000 to 30,000 EUR, depending on the number of systems and the complexity of the data mapping. The return comes from eliminating double data entry (3 to 10 hours saved per week) and making data reliable above 99 %. By removing billing errors, which often represent 1 to 3 % of revenue in disputes, the integration typically pays for itself in under twelve months.
What an API integration covers in 2026
An integration is not just "plugging two apps together". It involves field mapping, error handling, a retry queue, an audit log and monitoring. The price depends directly on the number of flows and their direction (one-way or two-way).
| Integration scope | Complexity | Timeline | 2026 cost (EUR) |
|---|---|---|---|
| CRM ↔ Billing (1 flow) | Simple | 4-5 weeks | 8,000 - 12,000 |
| CRM ↔ ERP (bidirectional) | Medium | 6-8 weeks | 12,000 - 20,000 |
| CRM + ERP + Billing (3 systems) | High | 8-12 weeks | 20,000 - 30,000 |
| Adding a dedicated middleware (iPaaS) | High | +2-3 weeks | +5,000 - 9,000 |
| Mapping to a legacy ERP (SOAP/CSV) | Very high | +3-4 weeks | +6,000 - 11,000 |
Modern REST/JSON APIs are the cheapest to integrate. A legacy ERP exposing SOAP, CSV exports or a direct database always inflates the budget by 30 to 50 %.
Hidden cost vs integration cost
The real comparison is not "integrate or spend nothing", but "integrate or keep paying for double data entry". Here is the 2026 order of magnitude for a 25-person SME.
| Line item | Without integration (yearly) | With integration |
|---|---|---|
| Double entry (5 h/wk x 35 EUR) | 9,100 EUR | 0 EUR |
| Billing errors / credit notes | 6,000 - 15,000 EUR | < 1,500 EUR |
| Late collection (DSO) | 4,000 EUR | 1,000 EUR |
| iPaaS middleware licence | 0 EUR | 1,200 - 3,600 EUR |
| API maintenance | 0 EUR | 1,500 - 3,000 EUR |
| Total | 19,100 - 28,100 EUR | ~7,000 EUR |
The extra maintenance cost is real but marginal against the losses avoided. That differential funds the integration within one fiscal year.
Mini case study
Take Claire, CFO of a 40-employee industrial SME in Lyon. Her sales reps enter orders in the CRM, then an assistant re-keys them into the ERP and rebuilds invoices by hand. Result: 8 hours of data entry per week, and roughly 2 % of revenue (90,000 EUR on 4.5 M EUR) lost to credit notes and disputes each year.
She invests 22,000 EUR in a CRM ↔ ERP ↔ billing integration over 9 weeks. Gains: 8 h x 45 weeks x 38 EUR = 13,680 EUR of recovered time, plus a drop in disputes from 2 % to 0.4 % of revenue, i.e. 72,000 EUR secured. Even counting only half of that dispute gain, the integration pays back in under 6 months.
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FAQ
What does the simplest integration cost?
A one-way CRM-to-billing flow (automatic invoice creation on signature) starts around 8,000 EUR for 4 to 5 weeks. It is the most common entry point.
Do I need a middleware (iPaaS) or custom code?
A typical iPaaS costs 1,200 to 3,600 EUR/year in licence but speeds up connection to standard tools. Custom avoids the recurring subscription but costs 5,000 to 9,000 EUR more to build. The choice depends on how many future connectors you expect.
How long for a three-system project?
Expect 8 to 12 weeks for CRM + ERP + billing, including mapping, regression testing and a 2-week pilot before full cutover.
What is the main risk?
Legacy ERPs without a REST API. They force SOAP or file connectors, adding 6,000 to 11,000 EUR and 3 to 4 weeks. A prior API audit avoids nasty surprises.
What maintenance budget should I plan?
Between 1,500 and 3,000 EUR/year for monitoring, keeping up with vendor API changes and fixes. That is what guarantees durable reliability above 99 %.
Let's scope your project. Tell us which systems you want to connect (CRM, ERP, billing), the direction of the flows and your monthly volume: we will price a precise scope with an indicative budget and schedule. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
