I'm on mastodon.art and donate $1/m, same story. It's only a handful of people that donate (hundreds, but still - much smaller than the thousands of users) and we cover the bill.

Though, this is also why i'm experimenting with custom Fediverse instance software that prioritizes low cost operation. I think Fedi would be better off if it wasn't a huge lift to figure out hosting. There's enough challenges in hosting instances, it would be nice to reduce as many as possible.

people may only donate when they can miss it

And because admins like you rock. If an admin is really cool, they can donate even their house, but if an admin is not cool, well... look at spez.

if every local user would donate 1 cent each month we would get more in donations than our total costs are

This is a really solid selling point. Every admin should do this math and ask for donations like this. I know I often fall into the trap of feeling like I need to donate more. Because it's a bigger bite of my budget, I end up procrastinating and not donating. But reading this, I would more readily donate an amount that's more comfortable to me but also accounts for other users' portions