Brake job on a 126 car - done in a shop that features competent MB techs - can run around $600-$700 U. S.
Chances are the rotors will be replaced - both front and rear, All four sets of pads and the sensors. A good tech will also repack inner and outer bearings(front) and replace grease seals. Go look up the parts prices of what I've listed & subtract from the figues above. There's your labor.
You ain't gonna get a turn-key 126 brake job for cheap and if you do, good luck.
The alternative is to do it yourself. Afterwards, you'll understand why a good shop charges what it does.
1991 300-SEL - Model 126
M103 - SOHC
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