Of course there's a cost. It's just - in my experience - a lot smaller, when you aren't forced to pay subscription fee along the way.

Example - I was working with jira server for several years at pretty small company. As business grew, there were better and worse moments and sometimes there were more important costs, than another yearly support fee.

Atlassian decided to drop this model and tries to force everyone to the cloud. They say that migration will take 9+ months.

That means if they ever do such change again it will take full annual cost of the license to get rid of them, with no option to avoid it.

You're always locked in, so you need to make sure that you can adapt it as needed. Either because you already own it (homegrown) or because you're prepared to take ownership if needed (FOSS done right).

For commercial software (or FOSS-as-appliance) then you're stuck going along wherever your vendor wants to take you.