For that price, I'd go with either a late 80's or early 90's model Suburban. Diesel swap, small lift, 35's. Take out the rear seats, add a whole bunch of electronic gizmos.
Sounds great to me. That, Or I'd throw all 15k into my XJ. Then I'd go with a 2.5in, maybe 3in lift, 31's, ARB Air Lockers front and rear, Rear Tire Carrier, StumpXJ-esque roof rack/RTT thingy, some lights, an ARB front bumper, and a nice winch, Im thinking a new Warn Powerplant just for the cool factor. Oh, and the requisite Safari Snorkel and dual battery set up. I figure I could source all that for about $15,000.
Oh, and an Engel 45qt. :snorkel: