lowereing the back is free, just adjust the springplates and beam adjusters for the front are about 30 bucks from acvw.net
what he said^^^^
in addition to that, in order to install beam adjusters, it will require you to remove and disassemble the beam, cut it, weld in the adjusters, and re-assemble and re-install the beam.
another option is buying and installing drop spindles. they will give you a set 2.5\" drop and will increase the front track by about 1/2\" (i think). this may or may not cause tire to fender clearance issues (ftr, you might run into the same clearance issues with the beam adjusters, depending on how low you go & what size tires you run).
imho, drop spindles are an easier install but you'll still need to deal with pressing out/in balljoints. they also cost a little more ($200 +/- a bit).
either way you go, dont forget a set of caster shims (to maintain proper caster after the drop)and other parts that may need replacing (beam bushings, tie-rods, balljoints).
good luck.