Bought my W124 rebuild at FastLane for $125...this was two years ago.
I also installed it myself. It's pretty much a DIY job. It's a bit tight for room to get at the mounting bolts, but deinstall took me about an hour.
Install was simpler...30 minutes including replacing the serpentine belt.
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