My job offers me the fringe benefit of sticking my server in the data center without much hassle. This is subject to change, but currently free. The only cost (besides my time invested in features of the site) is hardware replacement and improvement. The server hardware isn't terrible, but could always be better. Multi-core proc would be handy, more ram, and some disk space would be on the list.

That's about it, hopefully that answers your question.

PS: Donations of operational hardware that I can use would be acceptable..:P