I've still got my original chain and it has probably 45-5000 miles on it. Every once in a while I'll have them measure it and otherwise check it out. I certainly have no problems shifting. In January I had a good maintenance done. Got new cables, etc. I think that ran me around $100. I'll go through anywhere from 5-10 tubes a year plus a set of tires.

Your costs sound way out of bounds. & I really don't understand the need for a new chain and cassette very often.