I was under the impression that if the service is completed by the supplying dealer, then you only pay for parts, not labour. Any extra work involved in changing the final drive oil should not be part of the cost, only the small amount of oil used.
The 600 service to my 04 1200 was £36.58, which was £36.58 more than the same service on my 1150 back in 2002!
Mike