If you're considering one of the WJs, take a look at the WJJeeps website; lots of details on the different models and tons of info.
I'd suggest looking for a nice, clean 03 or 04 WJ since they have improved brakes and a computer that allows for more 'tuning'. I'd also suggest trying to find one of the more basic packages such as the Laredo-based 'Columbia' edition. Less electronic bells and whistles, more of the stuff you actually need. Ironically, the 'Overlander' edition is overly complex and lacks features you'll actually use. :smilies27 Be patient in your search! Good, low mileage examples are out there and can be had for less than $5K. Search CL using the term 'cherokee', omitting the 'grand'. Many are not posted correctly and you'll miss quite a few. Also, check the box on the top left of the page to 'include nearby areas'; this helps spread your search, too.
Yes, the 4.0 engine will last forever, but don't discount a 4.7 HO that has been well maintained. My WJ HO actually gets better mileage than my XJ ever got during the 300K miles I owned it. Just some thoughts!