Don't know much about replacing stock ball joints. I do know that you can pick up a set of UCA's from Dirt King for $575. Not much cheaper than PRG, but if you go this route just thought I'd give you a heads up that PRG has been experiencing shipping/customer service issues lately. The UCA's aren't bad to replace. The driver side is a bit tougher due to the brakes lines being in the way.
'07 CC 4X4
banks ram air w/ tb screen removed, banks monster exhaust, prg minilift, PRG UCA's, PRG endlinks, 5100's all around, DK shackles, EBC brakes, headlight mod w/ JB switcbacks, Legit 55w 6000 hid's (lows and highs), modded tail lights, street scene grille shell, xd diesel 20x10 w/ terra grapplers, pinch weld mod, axle vent mod, BW pocket flares, PD'd stuff, BL step rails, SM designs bezel kit