The verdict in three sentences
A client portal with an invoicing module in Berlin runs 45,000 to 100,000 EUR, plus 7,000 to 19,000 EUR for the ERP connector (Sage, DATEV, Odoo) and 4,000 to 11,000 EUR for 2026 e-invoicing compliance (ZUGFeRD/XRechnung). Online payment (Stripe, GoCardless) adds 3,000 to 8,000 EUR. Expect 10 to 14 weeks and maintenance of 800 to 2,200 EUR/month.
Pricing module by module
This kind of portal is an integration project as much as a development one: the value comes from reliable synchronisation between the ERP, the invoicing tool and the client area.
| Module | 2026 range (EUR) | Function |
|---|---|---|
| Portal + invoicing module | 45,000 - 100,000 | Invoices, credit notes, due dates, history |
| Connector Sage/DATEV/Odoo | 7,000 - 19,000 | Sync accounts, invoices, payments |
| Online payment | 3,000 - 8,000 | Stripe, GoCardless, auto reminders |
| 2026 e-invoicing compliance | 4,000 - 11,000 | ZUGFeRD, XRechnung |
| Reminders & DSO | 3,000 - 7,000 | Reminder scenarios, dashboard |
| Multi-company area | 5,000 - 12,000 | Groups, subsidiaries, consolidation |
Amounts = 2026 order of magnitude for a German SME. E-invoicing compliance must be scoped early because the regulatory timetable shapes the project.
Recurring costs and DSO gains
A well-designed invoicing portal reduces payment delays (DSO) by giving customers permanent visibility and one-click payment.
| Line item | 2026 range | Impact |
|---|---|---|
| Developer day rate | 450 - 720 EUR | Portal development |
| ERP integrator day rate | 600 - 900 EUR | Connector, mapping |
| Maintenance | 800 - 2,200 EUR/month | Changes, support |
| Hosting EU | 130 - 480 EUR/month | GDPR, backups |
| Total timeline | 10 - 14 weeks | Compliance included |
Cutting DSO by a few days frees up working capital often counted in tens of thousands of euros for an SME.
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Mini case study
Marc, CFO of a Berlin manufacturing SME (8M EUR revenue, 58-day DSO), commissions an invoicing portal at 68,000 EUR + a DATEV connector at 14,000 EUR + e-invoicing compliance at 8,000 EUR, so 90,000 EUR, maintenance 1,300 EUR/month. Thanks to automatic reminders and online payment, DSO drops from 58 to 48 days. On 8M EUR revenue, 10 days of DSO equals roughly 8,000,000 / 365 x 10 = 219,000 EUR of freed cash. Even valuing that gain at a 5% financing cost only, the annual saving (~11,000 EUR) covers maintenance and part of the build in the first year.
FAQ
Why integrate the ERP rather than enter separately? Without a connector, every invoice is entered twice, a source of errors and disputes. The connector (7,000-19,000 EUR) ensures the customer sees exactly the amounts in your accounting.
Is 2026 e-invoicing compliance mandatory? The reform progressively mandates electronic invoicing and formats like ZUGFeRD/XRechnung. Budgeting 4,000-11,000 EUR avoids a rushed compliance scramble.
Is online payment worth it? Yes: for 3,000-8,000 EUR it shortens DSO and cuts manual chasing. The cash gain often exceeds the cost in the first year.
Which ERPs are supported? Sage, DATEV and Odoo are the most common in Germany, but a custom connector can target any ERP exposing an API or structured exports.
How long to deliver? From 10 to 14 weeks, with e-invoicing compliance and the ERP connector forming the project's critical path.
Let's scope your project. Tell us your ERP, invoice volume and current DSO: we'll price a 2026-compliant invoicing portal in Berlin. 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.
