Custom ERP: the management system written around how your company works

When it makes sense (and when it doesn't)

A custom ERP makes sense when several of these are true:

• Your current ERP models your work badly: there are spreadsheets "next to" the system for everything important.
• You can't see real margins per customer or per order until month end, because cost data arrives late or by hand.
• You pay per-user licences and the number of users keeps growing — a generic ERP runs €150–200 per user per month.
• There is a shop floor, warehouse or logistics operation the ERP can't see.
• You customised an off-the-shelf ERP and every update breaks the customisation.

It doesn't make sense if your processes are standard and your team is small: a well-implemented off-the-shelf ERP is cheaper and faster. Nor if nobody in the company is willing to open up costs, margins and exceptions — without that, there is nothing to build.

What it costs

• Initial build of a custom system that replaces a generic ERP: €80,000–180,000.
• A reasonable first phase for a B2B company of 30–80 employees, replacing two or three critical pieces: €40,000–120,000.
• Keeping it alive (improvements, supervised AI agents, monitoring): €5,000–15,000 a month.
• First module live and connected to real operations: 8–14 weeks from signing.

And the cost of not building: licences of €150–200 per user per month, and €100,000–500,000 in consulting to get your data out when you change ERP. The full comparison is in how much custom software costs.

How it's built: module by module, starting with the one that hurts most

Nobody switches off an ERP on a Friday and switches on another on Monday. The first module is the one costing you the most margin, not the easiest one, and it runs alongside the old system while it's switched off piece by piece. The heaviest part isn't the code: it's documenting the exceptions. Every "we do it this way except when…" has to be written down before it becomes a rule in the system.

With AI agents inside

Because it's written from scratch, agents are part of the chain rather than an add-on: the order comes in, an agent decides what happens, in what order and who executes it, with your criteria and margins, and every step is recorded. With a shop floor, production data flows in on its own — see PLC, MES and ERP integration.

What it will demand from you

• Opening up internal costs, margins and prices per customer.
• Working with two systems at once while the old one is switched off.
• Documenting the exceptions that live in someone's head.
• Patience: it's the most expensive thing we do and the slowest to show results.

How we start

Always the same way. Day zero: an NDA signed before you show us anything. Then the Nexus team analyses your operation and delivers a report with the exact changes, prioritised by impact on your P&L. Then you decide. Nexus Elite AI is an engineering boutique in Barcelona: two people, no juniors, no subcontractors, and never more than seven clients at a time. Apply and we reply within 24 business hours; if there is no fit, we tell you in writing.

Frequently asked questions