Rear pads judging my ebay (yeah not an exact price) range from about $32 through to $145.
So we go in the middle which puts them at $78...Give or take a few bucks
Rotors...General price is around the $190 ea mark
Labour will be an hours work at $130...
So the price of $670 to replace them would be close to the mark.
What I would suggest is to get your son just to make a couple of calls querying the price of pads and rotors for the car from an auto parts store, then add on that $130 ish for labour and make a judgement call for yourself if that is over the top.
The same can be done for the fronts, seeing as they are due for replacement. Then you will know for yourself how much the cost would be....