Yep. I think my total annual cost for my forum comes to about $500. I spend far more on other indulgences and pastimes. For this small amount per year, I get to discuss one of my passions with thousands of other people with the same passion. It's a bargain!
Similar. The forum I admin is basically a passion project. I split the costs with my other admin and it comes to maybe CA$350 now. We used to get the odd donation from other members, too.
OTOH, if we were getting paid at appropriate rates for the time we put in (I'm an IT professional with 25+ years experience and the other has a background in IT as well), that would escalate quickly. Without us volunteering our time and skillset, the place would cost a lot more to run.
Closing up shop for us would not be my decision, though. I don't own the site, I run it on behalf of the community. We would have to decide both among the Council (what we call "Staff") and then probably have a vote of the general community. That said, if we both decided it was no longer worth our time and money, that discussion would have to happen. There's literally no one else on the site who can run the place and no one else has offered to contribute financially in a while though if we launched a fundraising campaign, we'd probably get some pledges.
My advice to an owner/leader wanting to pack it in? If the site is going dark, e.g. you don't sell it or get someone else to take over, then at least try to allow some "grieving" time for the community. Lets them look for a new place to meet and connect, say goodbyes, and so on.
My current plan for closing down would be to set things up so that our hosting has at least six months left on it at the time I announce and use that to gradually ramp down. Have farewell threads and that sort of thing, then maybe have it "frozen" with forums still online but read-only other than the "Farewell" forum for the last month or so.
And do support anyone who decides they want to take it on or start a new spinoff community. That's how we started. When the original Wondercafe announced it was closing down, we had several months notice and used that time to build Wondercafe2. The owner of the original WC (a Christian denomination, not an individual) was mostly supportive of that effort, even allowing us to use threads on the old site to do logistical and organizational discussions.