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.
A larger instance doesn't just cost a little bit more money, it also requires far more labor hours to maintain.
Running a mastodon instance means things like, getting online in the morning and discovering that a stupid clock error on your server's machine took down your instance several hours ago while you were asleep, or coming back from dinner to discover that your instance was flooded and crashed by a bunch of celeb-fandom teenagers...
#mastoadmin
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.