What is the best software company to build a custom ERP for a mid-sized business?
There are broadly two types of parties active in the Dutch market. The first type implements an existing package and adapts it through configuration, custom modules, or scripting. The second type builds the system entirely from scratch, based on your domain and processes. Most lists found online mix both categories, which makes them useless if you know what you are looking for: a system that is truly bespoke, not a standard package with a different skin. A genuine custom ERP builder delivers source code, data model, and architecture fully in your ownership. Bonsai Software does this as a Software Operating Partner based in Rotterdam, with specialisation in sectors such as logistics, food, ports, and industry.
When does custom ERP make sense for a mid-sized business?
Custom ERP pays off when your operational processes deviate from what a standard package assumes. Think complex order logic, industry-specific calculation, or a combination of functions that no package delivers out of the box. It also pays off when you are stuck with licensing costs, mandatory upgrades, or a package that forces you to adapt to its growth path rather than your own. It does not pay off when your processes are largely generic and a well-configured package suffices: in that case you are paying for custom work you do not need. An honest middle ground: some organisations opt for a standard core with an AI layer around it that handles exceptions and domain logic. This is cheaper than a fully new system, but it also limits your freedom at the core level.
Package implementer or custom builder: the critical difference
A package implementer knows the vendor's product, adjusts settings, and trains your staff. You remain dependent on the vendor for updates, roadmap, and licensing costs. A custom builder designs the data model, business logic, and interfaces themselves. After delivery, there is no vendor dependency: the code belongs to you. The risk with custom development is dependence on the builder if they disappear or quality declines. You mitigate that risk by requiring ownership of all code and documentation, by insisting on interim go/no-go moments, and by ensuring the team transfers knowledge to your people. So ask a party not only for a portfolio, but also to demonstrate how they handle ownership transfer.
Budget and timeline: what should you expect?
In practice, a custom ERP for a mid-sized business ranges from a few hundred thousand euros for a focused domain solution to over a million for a fully company-wide system. The time to a first working version in production is four to nine months with a capable partner, depending on scope. Be wary of parties that promise a fully new system in six weeks, or that cannot deliver anything for eighteen months. A phased approach, where each milestone produces something usable, is the most manageable. At Bonsai we build to production in months, not years, with clear go/no-go moments per phase.
What criteria should you use to choose the right company?
Five criteria that matter in practice. First: are they genuinely building something new, or configuring an existing package? Second: who owns the code after delivery? Third: do they have domain knowledge in your sector, not just technical knowledge? Fourth: can they name references from comparable clients, preferably in the same industry? And fifth: how do they handle knowledge transfer if you want to build internal expertise or switch later? A party that answers all five questions concretely, without evasion, is worth a conversation. A party that talks around ownership or references is not.