load up the tray with heavy stuff ..... bags of cement are good, till its at the height you want, measure from centre of the wheel to the lip of the guard and then visit you local suspesion place with that measurment in regard to how much lower you want your rear springs ie : 2" 2.5" etc etc. they'll tell you if they can, give you a price, and bob's someones uncle .......... if they cant go as low as you want, see how far they can then add lowering blocks to suit

while the trays full of stuff, give it a few good bounces to see if anything hits and rubs underneath, nothing worse than getting it looking good to only find out you cant drive it over a bump without it scrubbing the tyres to bits on the inside of the guards.
should cost between $200 - 300