>Every Fediverse instance I've used - and I've used quite a few - has been either so small that the total cost is a few dollars a month, or fiscally sustained by donations from users.

And that is somehow invalidating what I have said? Sure, if you have 10 users then your costs are going to be negligible and you can probably sustain it from your own pocket or donations.

But good luck running a larger/popular service like that. There are reasons why the more popular Mastodon servers had to stop accepting new users after the Twitter/Musk fiasco - it was simply not sustainable for the one-man operator crews.