I had thought about this a long time ago, but then a member stepped up and sponsored us for a couple years (vpinball.com). I really didn't want to charge because this site isn't about money, but no one participated at the time so I asked myself why was I doing this if no one acknowledged it. I finally pulled the trigger on the credits idea, and I'm glad I did. I really didn't like "forced participation", but that has helped a lot. Not everyone can make a table or backglass, but just telling an author "nice job", or starting a topic makes this place a little brighter.
This site (relative to other sites) doesn't cost a lot, but I'm also limited by our software AND my knowledge of it. We use Simple Machines Forum software which is free, and I believe open source. Other sites pay a license for their software every year. This can be a lot of money. I tried to make different levels for donators vs regular members, but I couldn't get things to work right between the levels. There is still a donate button in the upper right of the homepage if anyone is so inclined.