I don't think self-hosted versions of many of these tools exist. Are you suggesting you build them yourself? It'd take years and your time is worth far more than the money you'd save.
Which makes totally sense for large organisations but less sense for small ones where it could be easy to manage most services off a single box, provided that regular backups are made.
Consider git alone: you can run a small gitlab instance for free. You can do ci/cd off a jenkins instance. Ticketing systems are one of the oldest things around.
Some basics of system administration is all you need.