I paid $60 or so to have the AC in my W126 charged up form empty; R134. My friend paid $75 to have his W210 done.
So where does he get $400 to charge it?
I would talk to the dealer they are probably much cheaper, or another shop.
Also why is the AC empty? Was the leak fixed?
For the shocks $1100 is pricy but not to far off. Bilsteins are probably $90 a corner plus a few hours labor.
As for the belt squeking something is not right I would sudjest replacing the belt and checking the tensioner.