I suspect your alternator has an internal regulator (pity because it's a much less expensive repair).
Nevertheless, FastLane carries the rebuilt Bosch alternators for around $140 + $75 core charge. If you don't mind doing the work yourself, you can save a ton of $$$. Probably cheaper than taking your original to a shop to get rebuilt. The rebuilt unit out of the box looks brand spanking new!
If you choose to DIY, you will have to remove the sepentine belt to do the job properly...replace the belt while you're at it...$30.
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