I also did the work myself and paid $60 a piece for new front disc rotors, $49 a pair for the front disc pads, and $11 a piece for new wear sensors at my local MB dealer a few months ago for my '92 300TE 4Matic wagon. The replacement of the pads was easy, (need only a wrench for the caliper bolt, slotted screwdriver for the wear sensors, and a C-clamp to compress the caliper pistons), and after the learning curve on the first one, (@ 90 minutes as it was my first time with this car), the second was done is less than 15 minutes. As for the rotors though, I didn't have enough leverage to get the securing bolts off the back of the rotor, (they were REALLY stuck!), so I put that off until a time when I can get the car higher up than on the jack stands I was using. As for the bearings, it is my understanding that they do not have to come off when you redo the rotor, but you may as well since the rotors are off. If you do the rotors yourself, just remember to remove the protective coating from them before you install them.
Also, as with most parts, I would recommend paying the small extra and getting OEM, because you know they will fit. For example, the bolt holding the caliper is a throwaway type; the self locking threads are stripped on removal, so the pads come with new bolts which non MB pads do not. I suppose you could reuse the bolt and apply locktight, but why not just do it right.
If you have a shop replace the brake pads, rotors and wear sensors for all four wheels, I would estimate that it would cost between $650 - $800 U.S., parts and labor. All the more reason to do it yourself!