I had the same issue on my 07 1200GS (not A) about 6 months ago. Down here in the land of OZ the repair was quoted at $3300. A little searching on the web (including this forum) revealed that the ABS units in 07 GS's is a known issue, and you may have a case to argue with BMW.
I chatted to my dealer (procyles st peters for anyone local) about what I had found on the internet, and he was very helpful. He offered to speak to the importer to see if they would supply a new ABS unit at no cost.
The request eventually went to Germany, with the response being that "if the bike has been serviced by a BMW approved technician in accordance with the service schedule, a new part will be provided at zero cost".
Thankfully my bike met the criteria, and I got the repair completed for labour only (abt $300).
I would have a chat to your friendly BMW dealer ASAP.