I'm just a newb but I think my sentiments will echo most of the forum... Check the frame throughly for any rust. Minor surface rust is easy to take care of, anything worse then carefully consider or even pass on the Jeep. If the fender is the only problem I would say jump on it. It looks repairable to me but even if you need to replace the fender it wouldn't be too costly.
As a reference I paid $10,300 for a TX rust free, 2000 4.0, 5 speed, Sport trim, with hardtop, 96k miles. I'd gladly pay $6k for that Sahara if all I had to do was replace and paint a fender.