Mine's due the same in 2,600 miles (just done 30,000). I was not expecting a bill that large. Let me know how you get on. I use Wollaston BMW (Northampton).
I just paid £670 for an extended warranty (inc breakdown cover and with £250 excess). Not sure if that means I have to use main dealer servicing - I'll check. Not sure if the planned Eisenmann Race will cause a warranty issue either - shouldn't do but who knows?
Also, make sure they use the revised diff oil to stop the horrible noise in tight turns.