I basicly converted mine for FREE! A local rover shop gave me a set of OME 751 springs and a pair of D1 spring seats for free after I had some work done there. I found a set of 762 springs for $40 (the guy threw in a pair of 1 inch spacers). And I bought a used set of OME shocks off Ebay for $125 shipped. I then removed and sold my air springs on Ebay for $175 (only had 30k on them). The result, a 3" coiled lift. For ~ Free!
Shop around, trade, bargain... you never know what you'll come up with. I actually might have the 751s for sale.... Cheap.