they go for various depending on how old they are, i have one at the moment that i would personally not sell for less than 265 plus fees and im pretty sure thats kind of the going rate, i have seen a few go for around the 300 mark, also depends if your looking at the AM or LT, Am would be slightly more.
Any problems in the past ask and look out for, for that price range you should get a gat thats in a decent enough state if its a LT, expect a tiny bit of anno but as i said should be ok, someone else will be able to tell you more about problems.