ABS modules are not unknown to fail but can be repaired or second hand tested units purchased alot cheaper than new. The usual fault with abs modules is dry joints on the electronics inside the module which is a easy repair if you know what you are doing. Extracting theodule from the car and refitting is the most difficult bit.
@Roadster girl, I am not sure how old your car is, I assume that the mechanic has tried to communicate with the ABS unit via either software or hand held unit. Do you know which diagnostic port they tried?
The ABS unit can only be accessed from the 20 pin connector under the bonnet.