I'm seeing a bunch of posts today about how hosting a mastodon admin doesn't cost a lot of money, and first I want to say that this is true; you can run an instance on $10-20/mo entirely reasonably.
But I don't want anyone to forget that there is a labor cost in running and maintaining an instance. It's not just pushing a button and feeding in some money, it's also monitoring your server and keeping it secure and handling reports and doing upgrades and all fo that.
These are not unique to mastodon, however. These are costs of running a social media website at all - fediverse or otherwise.
You're running and managing a service. Other people will rely on you to keep that service up and running. That's a much higher cost than the dollars involved.