I haven't read all the posts but here are my two cents since someone emailed me and asked for it. I once mentioned a certain product on this site and I got a very nice "thank you" from the company after because it help add to their sales. Since you have such a large pool of professional artists drawing eager art students to this site, it seem to only make sense that you could sell space for a small amount of advertising if are needing money to keep it afloat. I visit another forum that does this quite successfully for photographers.
http://www.dpreview.com/forums/forum.asp?forum=1021
You just might see a profit in a very short time. And artists visiting your site for the first time will be more likely to participate. I know when my art video is done I would love to advertise here. Just a thought.
Morgan