The regulator runs around $140, and is simple to replace.
Just know that the door panels on MBs lift UP, then OUT when removing them. Other than unbolting the top door pull, and the door handle trim, everything should come out fine.
I've replaced both rear regulators on my 300E, and it's about a 2 hour job for a novice.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car