I am lucky in that there is a great independent alignment shop in our area. I've had all of my Benze's aligned there. Surprisingly, none were out of whack enough to cause problems except my '93 300CE. They found a worn control rod that when replaced solved all sorts of problems.
The alignments were done around $90 each car so $129 at a dealer sounds about right.
Anziani
'93 300CE 204K
'95 E420 124K