We work in a 60 mile radius. Any further, and we charge travel costs. We try to book 2 or more jobs for an area that far away and it generally works. We have a guy over here though that will do an "End of tenancy" 3 bed house for around 90 quid. He travels all over Germany to do Army quatrers and doesn't charge extra for distance.
I know for a fact, he did one recently for around 100 quid and it was at least a 340 mile round trip. Even if he did 2 on the same day, it would still be a rubbish day. We used to try and compete when we first started CC, now we don't bother. Just charge what we think is a decent price and go for it.