do some reasearch first. its probably best to do some research. (i know thats thrown alot around this site, but its true)
if you are looking at a 3" lift there are a few decent options for you, (i'm guessing cheaper is better)
first, is your jeep a V8 or I6?
if you have an I6, a great option is to run ZJ V8 coils and a 2.5" puck, and throw your front sprngs in the rear. this is called a 'front to rear' swap.. popular on jeeps and i've done a few. you will need the coils and spacers, (or another 3" ZJ lift spring, or an XJ lift spring around 4.5") and a set of shocks for 3" of lift. it would be good to put extended sway bar links on it, but i didn't. maybe a rear track bar bracket in the rear and redrill the front bracket. use all stock control bars. google 'ZJ front to rear swap' there are hundreds of threads
this is about as cheap as you will get. rough country has a kit for 400$ and it has lower control arms, IRO has one without control arms too.
do yourself a favour and stay away from those 3" budget boosts in the rear. you really shouldn't use any type of spacer in the rear. if you want one of those Ebay special 3" lifts, use the spacer up front, and swap those coils to the rear. best bang for your buck.
or you can spend the $$$ for a real kit. eitherway, on that setup, you can run 31s comfortably.
if you have any questions, fire me a PM. i've done just about everylift on a ZJ you can buy; twice