I would think $300-400 would be a VERY conservative estimate.
After standing my ground with MB, I was able to get my rear window replaced...they covered the bulk of the labor and materials, and I was out $340. And that's just for the rear portion of the top! They claimed there part of the bill was $1200 (mostly labor).
Prices on the internet for the rear portion ran around $300, but I believe it's closer to $800-$1000 for the complete top. And I have no idea what labor would run.
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