Until you get to 35" tires, your jeep generally has good axles for most off-roading. Get a lunchbox locker for the front and/or rear for around 300 bucks a piece and you can run 33's locked as long as your Ujoints are in good shape.
If you don't have a lot of $$$, you're in the wrong hobby. Get your head down to earth and fix what you've got. You can slowly build up your Jeep piece by piece - even stock they're pretty capable.
If you want a lift, it's going to cost you $$$, Tires that aren't bald or suck - $$$, upgraded axles? $$$
You need a rebuilt or JY motor that matches what you've got, or a different XJ preferably with a 4.0L engine - they run forever and are super common.
Start saving for sensible things first like the ability to actually drive, then while saving for upgrades, feel free to read and search in the forum.
'00 XJ - Somewhat modified
'01 Venture - high mileage, paid for, shut it