Well the price range definitely helps.
For that money, you should be able to fine a decent XJ.
I'd narrow your search a bit and stick to anything '91 and newer. They have the High Output engine and better electronic engine controls. '96 and up have better axles (Dana 30 front with larger 297 joints, and a Chrysler 8.25 29 spline rear axle) and the engine management system went to OBDII which is fairly uniform among vehicles now.
When looking at potential XJ's, ask about it's "heritage"...... where it came from, how many owners, etc. XJ's that originally came from back east don't generally fare well where rust is concerned. Floorboards below the carpet and under the rear seat is the problem area. Look at the roof line at the corners above the windshield for rust bubbling.
Unless the owner has meticulous maintenance records for a lengthy time, I'd stay away from XJ's with over 200K miles.
If you find yourself drawn to an XJ from '90 and earlier, give the unibody a good look over - looking for cracks in the unibody. Do a search here and you'll find a few threads with pics of typical cracking issues.
Rear main seals are generally the most common oil leak source - most XJ's are going to have a leak there. Most XJ's "mark their territory"......
Feel free to post up any Craigs ads of XJ's you're interested in - we'd be glad to help you come up with questions for the owner. :thumbup: