In reply to TonyB:
The vast majority of climbers simply wouldn't get any benefit from a thinner or thicker rope. That's before you get onto the fact that measurement of diameter is not controlled properly so manufacturers can near enough say its a thick or thin as they want.
There don't seem to be many deals around lately for 80m ropes, I was looking around Christmas and ended up going for a green decathlon one. I've had several over the years and they're fine, and I've always bought the cheapest I could find.