The domain by itself is probably only worth reg fee, but since it was developed before and looks like it has some current traffic coming in as well as some backlinks (I'm showing Alexa at a little over 3m and 1400 backlinks) I'd guess you could get somewhere between $100 and $200 for it. I'd suggest doing a google search for a proxy script and slapping something up pretty quick so you don't lose your page-rank and and backlinks. The incoming traffic is going to decline every day unless you put SOMETHING up, and there are a lot of proxy scripts out there. People are always looking for proxy servers.