Did them myself so I'm not sure what a mechanic would charge. Of all the things I've replaced on the LS this was probably the most diffiucult.
Difficult because it was time consuming and tedious. The driver's side nut I could only turn a 1/4 or less at a time. Lying on my back with my hand all contorted was just a pain to me. But if I can do anybody can, IMO.