pretty cheap, plus you get new shocks. I would suggest taking the time to look over this forum as there is more information on this topic than you could imagine. There are plenty of reviews and ratings of the different types of lifts. Keep in mind, with lifts you pretty much get what you pay for. Meaning, the more expensive the lift, the higher the quality. The kit i linked to is an add a leaf kit. Usually not the greatest option if you already have sagging leaf springs.
99 XJ Sport, Rubicon Express 3.5" Super Flex, JKS adjustable track bar, 15x8 chrome cragar soft 8's, 32x11.50 BFG AT, OME Nitro Charger Shocks, hacked front fenders