I am saving towards a set of full size truck axles for my 88 YJ currently running 3.73's with 33's. I'll be doing a spring over with probably 2' leafs and 4.88's or 5.13's on 36" or 37 "tires.

Here's some things to consider as additional costs from your initial cost to purchase the axles. Unless your buying the set with the gear ratio, lockers, etc.. that you plan on running.

Ring and Pinion (2 sets) $400
Installation Kits (2)
Detroit Locker (Rear) $350-$500
Posi/LS/Selectable $300-$500
Bearing and Seals
Labor $550-$650

What I'm saying is that most who upgrade their axles will incur the latter costs.