I rode 9000+ miles last year and I went through:

3 Cassettes (9 speeds)
3 Chains
3 middle chainrings

I need to change them altogether or else I get chain slip which is dangerous and has led to one accident. Basically when i change the chain I need to change the cassette and the middle chaninring.

There are complications in so far as that if I keep on going with one chain I will accellarate the wear on the large chainring which is an expensive option. I can last a year without having to change the large ring if I change my chain when my Park tool tells me to (1% stretch).

Like everyone else that does high mileage I want to keep costs down but is running for AS LONG AS POSSIBLE on one chain a false economy?

I'd really like to get this sorted as I don't know which is the best way forward. In my experience there is not a great deal of advice for high mileage riders where, in this instance, riding with one chain for as long as possible causes more wear on other components (the large chainring). I think cervello48 has asked quite a searching question.