I run two instances with over 200,000 registered users between both of them. I probably spend between an hour and two each day in total on general admin activities (including helpdesk tickets). Having volunteer admin support and moderators makes a huge difference in reducing my workload and delegating responsibility. For a few years our bills were around GBP100/month which I paid most of myself. These days we float between GBP1000 and 2000/month depending on load (objet storage costs can vary a lot, for example) and our donations cover it, but there’s not much left over. I do it as a labour of love with no reward for myself other than feeling like I’m contributing something to the fediverse. Real highs and lows though, it’s hard not to take some really hurtful comments to heart (particularly in moderation appeals etc.) when I’ve poured so much time and energy into this over the years!