As of 2022-11-18 our instance costs $49 USD per month.
That pays for enough capacity with our hosting provider, masto.host, for about 500 users.
I operate this site, The Pub, out of my own pocket, gratis. This site runs on my own infrastructure where I host my other sites. The additional cost for one more static site is negligible. I consider hosting The Pub part of my contribution to our community.
As of 2022-12-16 I currently receive recurring donations from 12 supporters for the upkeep of the server. The rest of the costs are born by me.
I maintain a spreadsheet of donations and expenses. I update the spreadsheet at least monthly. I share copies at least monthly, tagged with #finances.
I accept donations via Liberapay. Liberapay organizes donations as if they are recurring but allows payment to be made all at once or in a few payments. They include information of the fees taking by payment processors with each option. I prefer Stripe as a payment processor but support Paypal since it works in more places.