craigslist, great tip! that's what I do, I actually put other car brands on my vehicles, run the tires out, sell them off and make some money. I've also purchased cars, taken the rims/tires, put stock junk back on, just to sell the car off.
I'm running a pair of 19" Mercedes Benz rims on the rear of my element right now. with 18" Mustang fronts.

I also have a good friend in the tire business, so that helps too (but surprisingly, I use my tire/rim trick). just purchased brand new Ruff rims for 3 bills, and I'm taking the tires off a set of mini cooper rims, then selling the cooper rims back on craigslist.

I also pickup rims/tires for $35 each from a tow yard. that helps with the 300zx, which I DESTROY rear tires on weekly.

rats, what year jeep? you have a 5x4.5 or a 5x5 lug pattern. you can cross reference here:
http://www.discountedwheelwarehouse.com/Jeep___Vehicle_Bolt_Pattern_Reference.cfmpics: tire stash, purchased a civic to steal the rims, element on 19s/17s temporary, 4x4 explorer with jeep rims, 300zx.