Assuming it is completely necessary, stay away from manufacturers dealerships for having unit replaced.
I had to replace the right hand unit at AU$1000 (by a GM dealership) after a diagnostic showed failure and the ABS/TC warning lights appeared a few days after I had the disc rotors and pads replaced.
The ABS/TC warning lights still come on and the ABS engages at low speed (eg, intersections and parking), indicating the unit was never at fault (and the service center couldn't identify any failed component either before or after removal of supposed failed unit).
I would (now) get 2nd (or 3rd) opinion before replacing any component and these forums are an excellent source for others' experiences before spending $$ on unnecessary repairs.
stuart
March 2010
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.