The verdict in three sentences
If your team re-keys more than 200 orders a week between the webshop and the ERP, a custom REST API pays off in 2026. Budget EUR 12,000 to 25,000 excl. VAT for six bidirectional flows synced every 5 minutes, delivered in 8 to 12 weeks. The real cost driver is not the code, it is the data quality in your ERP and how well its API is documented.
What an ERP to website integration actually covers
A serious integration does more than push orders. It handles six flows, each with its own direction, frequency and conflict rules. An IT manager in Amsterdam should list them in the specification before asking for any quote.
| Flow | Direction | Recommended frequency | Complexity | Indicative 2026 cost |
|---|---|---|---|---|
| Customers (B2B accounts, addresses) | Bidirectional | 5 min | Medium | EUR 1,800 to 3,500 |
| Items and product data | ERP to website | 15 min or on change | Medium | EUR 2,000 to 4,000 |
| Stock per warehouse | ERP to website | 5 min | Low | EUR 1,200 to 2,500 |
| Prices and customer discounts | ERP to website | 5 min | High | EUR 2,500 to 5,000 |
| Orders | Website to ERP | Real time or 5 min | High | EUR 2,500 to 5,500 |
| Invoices and credit notes (PDF) | ERP to website | Daily | Low | EUR 1,000 to 2,000 |
| Monitoring and error alerts | Cross-cutting | Continuous | Medium | EUR 1,000 to 2,500 |
The most expensive flow is almost always B2B pricing: price lists per customer, discounts per product group, negotiated net prices. Exact Online exposes a well-documented REST API, which keeps budgets at the lower end. With older on-premise systems (Exact Globe, AFAS, SAP Business One with custom fields) where you must rely on CSV exports or direct SQL reads, add 20 to 30%.
Quote: off-the-shelf connector, middleware or custom API
Three architectures coexist in 2026. The right choice depends on volume, how specific your business rules are and how much vendor lock-in you accept.
| Criterion | Off-the-shelf connector | iPaaS platform (middleware) | Custom REST API |
|---|---|---|---|
| Upfront cost | EUR 1,500 to 5,000 | EUR 5,000 to 12,000 | EUR 12,000 to 25,000 |
| Recurring cost | EUR 50 to 200/month | EUR 300 to 900/month | EUR 80/month monitoring + hosting |
| Specific B2B rules | Rarely handled | Partially | Fully |
| Setup time | 2 to 4 weeks | 4 to 8 weeks | 8 to 12 weeks |
| Lock-in | Connector vendor | iPaaS vendor | None, code handed over |
| 5-year cost (estimate) | EUR 4,500 to 17,000 | EUR 23,000 to 66,000 | EUR 17,000 to 31,000 |
An off-the-shelf connector is fine for a simple catalogue with public prices. As soon as you sell to businesses with account-specific terms, it breaks or forces manual workarounds. iPaaS is attractive, but its subscription overtakes the cost of a dedicated API after about three years.
Timeline and milestones of a typical project
A well-run integration follows five milestones. Weeks 1 and 2: ERP data audit, field mapping, conflict priority rules. Weeks 3 to 6: customer, item and stock flows. Weeks 7 to 9: pricing and order flows, the core of the project. Week 10: acceptance testing on staging with 500 real anonymised orders. Weeks 11 and 12: phased go-live, 5 days of parallel control entry, then manual re-keying stops.
Monitoring is the line item SMEs forget. An order rejected by the ERP because of a missing VAT code must trigger an email or Slack alert within 10 minutes, with an error dashboard. Expect around EUR 80/month for monitoring hosting, logs and light corrective maintenance.
Mini case study
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Sanne, IT manager of an industrial supplies distributor in Amsterdam, handles 300 web orders a week. Two assistants re-key them into Exact Online: about 2.4 minutes per order, or 12 hours a week. At a loaded cost of EUR 32 an hour, that is EUR 384 a week, roughly EUR 18,400 a year over 48 weeks. Add the errors: 2% of orders entered wrongly, 6 a week, each costing about EUR 45 to correct and credit, close to EUR 13,000 a year.
The chosen API costs EUR 19,500 excl. VAT plus EUR 960 a year for monitoring. Estimated annual gain: EUR 31,400. Payback: about 8 months. The two assistants now follow up on unconverted quotes.
FAQ
How much does a REST API between an ERP and a website cost in 2026?
For an SME, expect EUR 12,000 to 25,000 excl. VAT for six flows. A scope limited to three flows (stock, orders, invoices) can come down to EUR 7,000.
Do we need real-time sync?
Rarely. A 5-minute sync covers 95% of B2B needs and costs much less than an event-driven architecture. Real time mainly makes sense for very fast-moving stock.
What happens if the ERP goes down?
The API queues orders and replays them automatically once the service is back. No order is lost, and an alert fires after 15 minutes of downtime.
Who owns the code?
Under a well-drafted contract, you own it outright on delivery, with the Git repository, OpenAPI documentation and hosting accounts in your name. Insist on that clause before signing.
Our ERP has no API. Is that a blocker?
No. We can read the SQL database or process scheduled exports, at a 20 to 30% premium and sometimes with a 15-minute sync limit.
Let's scope your project. Send us your list of flows, your ERP and your order volume, and we will price the scope, indicative budget and go-live plan. 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.
