For twenty years the default advice to small businesses was simple: buy SaaS, never build. AI coding agents have changed the cost of building, but not the cost of maintaining what you build. The right answer is still usually a mix: SaaS for what is generic, custom software for what makes your business different. This guide helps you decide which is which.
The short answer
Buy SaaS when your process is the same as everyone else's and the product fits it without workarounds. Build custom software when the process is what sets you apart, when you are paying for many tools that do not talk to each other, or when no product fits without forcing your team to work around it.
A decision table
| Question | Points to SaaS | Points to custom |
|---|---|---|
| Is the process standard in your industry? | Yes (payroll, email, accounting ledger) | No, it is how you compete |
| Does a product fit without workarounds? | Yes | Only with spreadsheets on the side |
| How many tools does the process touch? | One | Several, with re-typing between them |
| How fast do your needs change? | Rarely | Often, and the vendor's roadmap lags |
| Who owns the data model? | The vendor is fine | You need it to fit your business exactly |
| Do you have someone to maintain software? | No | Yes, internally or with a provider |
| Seats and usage | Few users | Many users on per-seat pricing |
If most answers land in the right-hand column, custom software deserves a serious quote.
Is custom software cheaper than SaaS?
Sometimes. Custom software costs more up front and less per user over time, so it tends to win when you have many users, several overlapping subscriptions, or a process that SaaS forces you to work around by hand.
The only honest way to compare is a total cost of ownership over the same period, usually five years:
| Cost line | SaaS | Custom software |
|---|---|---|
| Up-front | Setup, migration, training | Discovery, specification, build, migration, training |
| Recurring | Subscriptions × seats × years, price increases | Hosting, maintenance plan |
| Hidden | Workarounds, re-typing between tools, add-ons, integrations | Changes as your process evolves |
| Exit | Data export, switching cost | None if you own the code and the data |
Fill in both columns with your real numbers: subscription invoices, number of seats, hours spent re-typing data, and a fixed-price quote for the custom option. The comparison is usually clear once the hidden lines are counted.
What AI changed, and what it did not
- Building got faster. AI coding agents write most of the code, so a focused business application takes weeks rather than months.
- Prototypes got cheap. You can see and click through the custom option before committing to it.
- Maintenance did not disappear. Software still needs security updates, fixes and changes. Plan for it from day one, or the custom option will cost you later.
- Quality still needs an engineer. AI speed without tests and review produces software you cannot trust; see Is vibe coding bad?.
How much does custom software development cost?
Custom software cost depends on the number of screens and roles, the integrations, the data migration and the level of testing and security required. The only reliable number is a fixed quote after a short discovery, which is how we price every project.
What drives the price, in order of impact: the number of systems to integrate, the data migration, the permission model (how many roles see what), and the number of distinct workflows. The look of the screens matters least.
Two real cases
Our own ERP replaced an invoicing SaaS. We used an off-the-shelf invoicing tool, separate from our client records and pipeline. Since September 6, 2026, our internal ERP issues quotes and invoices itself, next to the client records, pipeline, bank matching (proposed by the software, validated by a person) and the work of our AI agents. One data model, no re-typing between tools.
A legacy system replaced by a web application. A French debt-collection agency ran on a 1990s desktop application with no API, built around its own way of working. We are rebuilding it as a web application, sprint by sprint, with its data migrated. Details on legacy software modernization.
Should a small business build a custom CRM?
Build a custom CRM only if your sales or service process is genuinely different from what CRM products model, or if the CRM must be one with your operations (orders, projects, invoicing). Otherwise, a standard CRM plus integrations is cheaper and faster.
A common middle path: keep the standard CRM for contacts and email, and build a custom application for the part of the process that is yours, connected to the CRM through its API.
Next step
Bring the list of tools you pay for and the process that frustrates your team. In 30 minutes we will tell you whether a custom build is worth quoting. For the offer itself, see custom software.