Expect to pay anywhere from $250 to $400 in labor. I had one place quote me a cost of $600. Some places I've checked will only work on the rear end if it's removed from the car.
It's a tedious job, and I'd be suspicious if a place really low-balled the price.
ask around at a car show or test and tune, you might find a mechanic that does it at his house on the side cheaper. i got mine installed for $150 that way.