The evaporator is part of the a/c system, and MB buries it under the dash in W124 and W140's, in particular.
The part can be between $600 and $1,000, but the real killer is the labor.
It's 15.5 hours to replace one on a W124, and over 20 hours on a W140.
The whole interior of the car in front of the seats has to come out to replace the evaporator. Apparently MB never expected these to go out because they put it in a very hard to replace area. A huge engineering error.
And for some reason, early model W140's are notorious for leaking evaporators.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".