The tow prep package is $250 if you get it on the vehicle when you buy it. This gets you the wiring harness (I have read in other threads that it is not installed), the oil cooler (installed), and a full size spare tire.
Here is the oil cooler
if you want to DIY. My local dealer sells the same part for $165.
There is no reason (IMO) to pay for the OEM jeep kit. You can get the trailer wiring
at etrailer.com for $65 or under.
Of course this is all only the tow prep, so you'll still have to add the hitch.