Replace the rotors or can they be machined?

[Nakattack]

Well, I have an 06 4.4 with 57k on it and the rear pads and sensor need to be replaced. I have replaced the pads on my 01 530i and my 95 M3 before. Well, I have researched the forum and have read a few things in other places, but can't really seem to find something about if i can get the rear rotors machined? I have heard the rotors will be fine if I have enough of it left, 10.5 I beleive. However, the dealer says replace them fully. I obviously want to do it right and at the same time, not waste money if I don't have to. I have gone to a "popular" bmw part store online and they are looking at 108 for each rotor. An auto parts store will machine each rotor for 15 bucks. I have the time, but I need a few opinions here. The stealer said 644 bucks for rear pads, rotors and the sensor. lol. what a joke.