Gitlab's aim seems to be to replace the mashup of multiple 3rd party systems into a central place for the company. The associated costs of each one of those systems, user management, etc that go with them adds up.
Plus, you have to consider any per-user pricing as part of your cost per employee. If you're paying somebody a salary who's accessing a system where they interact with the rest of the company...$29 is not a big deal when lumped in with the salary, benefits, taxes, etc.
If you're a few college students working in your spare time with no income, sure it's a problem. But even then Gitlab gives away plenty on the free tier and you can each setup a runner on your own laptops to avoid paying for CI minutes.
IMO, this pricing is very reasonable considering the variable quality of different integrated systems out there.