Q&A

 Journeyman

This would require a diagnosis to determine the cause of the problem, and only then can an estimate be provided.

 Rookie

It could be the Heater Blower Regulator. Simple to replace, costs about $60 on Ebay. When you have the blower motor exposed, spin the blades by hand. If they don't make any squealing noises (as they would if a bearing was bad) then your motor is probably good. The blower regulator comes with a small tube that looks like a miniature tube of tooth paste. Don't use it for that! It is heat sink paste (zinc oxide). Remove the old regulator - there are two small screws that hold it on to the blower motor. (A magnetic screwdriver can be a big help here.) Then disconnect one red and one blue wire that go to the blower motor and a square, 4-pin connector. Remove the old regulator. Connect the new one. Take the heat sink paste and smear a lot of it on the base of the regulator so it covers it completely (It's the square metal plate the regulator sits on). Screw the new regulator back on to the blower motor with the two screws you took off before. That should do it. I replaced mine and saved $1200 the MB dealer wanted to charge me for installing a new blower motor. While you have the blower motor exposed is a good time to change the cabin air filter.