For $5000 you can have a brand new 500 cc 4x4. Actually a bit less money, $4900 I was told. That is the way I would go if that is your price range. 4 wheelers are less money now than they were 3-4 years ago. We bought a brand new 2008 700cc "x2" Polaris this spring for $6K including all taxes and fees.

Some used 4 wheelers are hardly ridden, some have been abused mercilessly. One day last spring I drove past a mudhole with some 4 wheeler guys playing, they were taking turns running through with only the handlebars sticking out. I would not want to be the next owner of one of those units!