There is no cheap or easy way to put 36s under an XJ. This is from someone who has done it.
XJs are unibody so body lifts are out. You'll need a suspension lift of 8". After 6" of lift the factory suspesnion geometry gets messed up so long arms are highly recommended. 33s are the safe limit for the stock axles, 35's can be done, but not for long. People who argue this point just haven't wheeled to the fullest capacity of a 36" tire. Past 35s with stock axles is just begging to be "THAT GUY" on the trail.
XJs are leaf sprung in the back so its pretty easy to swap in a different axle back there. The front is another matter. Fronts are coil sprung like a TJ so an axle swap for the front requires quite a bit of fabbing and welding. Also frame reinforcments are a good idea for running 36s as the unibody will start to flex.
36's will also require extensive cutting of the body to retain flex.
Bumpers aren't easy either as they need to be tied properly into the unibody frame to prevent ripping out.
Past 33s ripping the steering box off the frame is a definte possibility so think about ram assist and bracing the box/reinforcing the frame.
To properly build an XJ for 36s and be reliable budget $5000 minimum, not including tires or cost of rig. This takes in account a long arm kit, d44 front axle, high steer, replacement rear axle, bracket kit for front axle, brake lines, and assumes you can weld/fab as needed yourself.
Some sites for research:
http://www.naxja.org -the definitive site for XJs
http://www.claytonoffroad.com/ -the best and strongest(and most expensive) long arm lift kits for Cherokees
Not sure what your background is but an xj with 6" of lift, 33s and front/rear lockers is an EXTREMELY capable rig and WAY cheaper/easier to build.
Also in my opinion the 5psds offered in the XJs are junk while the AW4 auto is almost bullet proof.