I have a 1990 Diesel K1500 and the only hard part about the job is actually taking off and putting the wheels back on (6 lugs and the factory aluminum wheels seem to weld themselves to the hubs every time). I timed it and it took me just over 7 minutes to remove the caliper, compress pistons with a cheap hand-screwed compression tool, remove pads from caliper, replace pads in caliper. Then it took less than 5 minutes to replace caliper onto rotor and mounting plate.
Removing the wheel took 10 minutes because it was bonded to the hub and replacing it took 5.
The $600 price is probably based upon the fact that they must disassemble the auto-locking hubs on the front of 4x4s in order to remove the rotor which is mounted BEHIND(!?!) the hubs. This job is a MAJOR PITA and takes a couple of hours due to the time spent ungreasing and regreasing the autolocking hub components - and untorqueing and retorqueing the &^%$# great big sort of castle nut inside the hub. It requires a special impact socket with tabs to engage the "castle" nut's slots. Even the rotor job is not so hard, it's just greasy as all hell and time-consuming. This 1990 Suburban is a diesel, though, and as such has the same brakes as a 2500 (apparently).
My 1999 Diesel K2500 is easier, but the *&^%$ rotors seem to be welded onto the hubs (heat + moisture * 1000's of repeats = permanent bond).
Ace