Hi AWM,
I just had my cassette and chain replaced -- and the shop said it is common to need to replace it when you have around 3000 miles on the bike. I have 2900 on my bike. I also had the derailler replaced, since apparently somehow it was damaged. Cost $50 for the cassette and chain. $45 for the rear cassette which was an exact replacement of the one on it.

I trust this bike shop 100% and was having some shifting problems, so I feel they were not "taking me for a ride".

How many miles have you ridden with this bike?

Barb