Try a company that re-arches springs, cheaper. IN Somerville Massachusetts there is a place called Duff springs and they re-arched and rebuilt the springs in my hot rod for $100
Call Tom Laher at HellCreek Suspensions http://www.hellcreeksuspensions.com and ask him if he'll sell you just the springs. He is the owner who also manufactures his own springs. Really nice springs.
If they are sagging on one side you'll have to replace all 4, or they'll still be uneven. Unless your jeep has the same spring all the way around, then you can move springs end to end and side to side until it sits fairly level.