Perhaps you could get a new lock at a junkyard and then take it it a locksmith to have it made to fit your key.

This should cost less than $150, but I'd call the locksmith first. Mercedes keys and locks are not standard after 1990.

There is certainly nothing in a doorlock that should cost that much.

__________________
Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)