Sorry to hear about all the BMW service rip offs, it seems they are taking advantage of mechanical virgins.
I can think of hardly any service work which could not be tackled by many owners, including brake bleeding of the abs system. I bought a pneumatic bleeder 20 yonks ago and it works fine on super duper car abs systems. It just needs 10bar air from my modest garage compressor, and sucks the bubbles, along with all the crud, out of any circuit in 10-15 seconds
A good set of suitable tools and a manual could be bought for £400 and you then have the satisfaction of knowing it was done correctly. Not always guaranteed down at your local dealer.
Incidentally, does Haynes or someone do a manual for current or earlier GS and is it any use? From what I have read the BMW cd seems a bit short on detail?
Terry