The price of used jeeps vary, depending on what region you live in.
You'll need to check around in your area and see what they going for. After that, then treat it like any other used vehicle, test drive it, check it out, have a jeep mechanic check it out, etc, etc. The ad says it was never been off-road, so check the under carriage for damage. Also, find out who did the mods and have the mechanic pay extra attention to them. Always remember, when you buy a used vehicle, you just may be buying someone else's problems.