Sounds like a good deal. I recommend you go to ebay motors and take a look at what they are selling for around your year and mileage. Do the same with craigslist. I'm actually getting ready to jump head first into a 00' XJ with 115k miles for 5k from a used car dealership. I've been looking at them for a while. I think $6k (just $1k less than the 2000 I'm looking at with 115k miles) is a great deal.
Also remember to check the oil for coolant before & after your test drive. It'll be a milky substance on the dip stick. Some 99 XJs suffer from a manufacturing problem in between heads 3 and 4 that can cause microcracks in the heads or the gasket. If the casting number has the double 3's, that could be a good negotiating point to argue for a lower price or a 30 day warranty on the bill of sale. If your coolant is a light brown, it might just be very old.
Also, I asked the same question your asking. A lot of people have told me that the north east uses a lot of salt on the roads so thoroughly check out the underside of the jeep. If the rust is already at the nook and cranny stage, don't go for it. It'll probably be rusted out shortly. If its just discolored, you can use rust preventative.
Last edited by LowTread; 10-22-2013 at 02:10 AM.