That is outrageous. Like more than double what it should cost for just the rears. Was this a dealer (if so, which one) or a local shop?
There's no need to pay more than $75 for rear pads on a DD. Stock pads or something like Centric PosiQuiets will be fine for street use. If you have the sport package, you don't even have to remove the calipers to change the pads. Either way, installation shouldn't cost more than an hour labor or so ($80-100 depending on shop location).