This fundamentally misunderstands a couple of things.

DIY software is "free" like a free yacht is free. It initially looks appealing but there's a lot of expensive hidden costs and upkeep and pitfalls and problems.

For one, this is a bad assumption:

> building something that fits your actual needs

Unless your business is very small and not growing, this is a moving target. Your needs are going to change as you grow and different groups in the org are going to have different needs.

You really don't want to be dicking around creating software that already exists instead of doing the shit that actually makes you money. Spending a few hundo thousand on a bunch of software is nothing, you spend that on one engineer.

You buy a SaaS product because you have a problem and want to throw money at someone else to deal with it.