I'll take that back. I didn't realize they replaced the Blower assembly as well. $522 sounds about right for a dealer. However, I'm confused on the additional motor. Maybe that's a typo and is supposed to be the regulator.
Parts prices set aside, the labor seems very high. $705 for a brake job. What did they do? Rebuild the calipers. Shouldn't take more than 2 hours to change rotors and pads.
Next time find a good independent and order the parts from Mercedesshop.

Vin