I paid $35 a pair for S10 rear springs at a junkyard - that even included them torching them off rather than me trying to break old spring bolts free. Worked great for two years of abuse until I broke a spring. I recently got new lift springs up front and the ride is so much better (and my Jeep is a trail only Jeep) in the front than the back that I am going to be buying the same springs for the rear now.
The springs are the 3.5" Fabtech springs from Amazon - only $65 each, but they do not come with bushings so about $100 a corner.
1994 Jeep YJ : 3.75" of lift, 4.56 gears, 8.8 w/ lsd, 34X10.5 TSLS and some other stuff. 4 Angry Squirrels and proud!
1981 (with some 80 and 84 parts thrown in) CJ7 under restoration. SBC 350, 2.5" lift, half hard top and lots of fun!