$225 to replace the strut mount is ludicrous. You do not have to remove the strut in order to replace the strut mount.
To do it yourself you'll need a large hex key (forgot size -- 5mm?) and an open 22mm wrench. (size for my 300E, not sure if same for your MB)
Remove tire. Jack the car up on the broken strut mount side high enough to place a jackstand underneath the A arm and lower slowly to compress the strut more than the natural weight of the car would.
Now hold hex bolt (on top of strut) in place while unloosening the 22mm bolt that holds the mount on. If the strut begins to recess downward as you're undoing strut bolt, then you'll need to lower the car jack to put more pressure on the strut/A-arm, while keeping jackstand in place.