Am I getting screwed for my car (brake) repair?

My rear brakes on my Volvo C30 started leaking brake fluid (not under warranty). I brought it to a mechanic (Sears Auto - I have used them for some other minor stuff and like them for the most part) and he said the rear caliper was bad, which I expected. He also said that the whole system needed to be replaced on both sides. This would be calipers, rotors, pads, and a few other misc items. About $850.00 worth of parts/labor. Is it common to repair everything for one caliper issue? I have already authorized the work to be done so I don't know if I can get out of paying for the parts/work.Anyway, any information is welcome. Thanks! via /r/cars http://ift.tt/2taSDvR