Most of us who have modified rigs agree that a lunchbox locker would be the best mod to start with if you arent going to do a gear change. If you go with a lunchbox locker, they are cheap and easy to install.
let me give you a scenario...a few yrs back I went wheelin' a place called los coyotes which has some terrain from mild to wild. We met up with some dudes
who were camping there and rode the trails with them for the day. Now heres
a comparison between my rig and one of the guys rig we were with. Mine being a Ranger with about an 8" SAS, 35" tires and no lockers...just a limited slip in the rear. The other guy had a bone stock IFS toyota truck with street tires that were probably not even 31's and no kind of lift. This guy was all over the place with his Toy that I wouldn't even think about going simply because he had lockers, plus with no lift he had a very low COG.
For 2k you could probably do a lunchbox locker, buy a used lift off the board and new tires. That would make your rig plenty capable for medium class trails. From there, you can build it up..engine/exhaust mods, wheels, rock sliders or whatever but at least you have a working foundation to build from.
Take it from me, i'm on my 3 lift and spent a lot of money I wish i had back in my pocket or at least to have to spend on other goodies for my rig. Take your time and read up on what others have done and make sure you are going to be happy with the lift and tire size you choose...believe me, you'll always want more.