This topic is a common one on long distance hiking forums. On the Appalachian Trail, for instance, costs vary from $1 to $5 per mile. And a huge unknown is rate of travel--a fast hike/ride is a cheaper one. An older traveler will probably spend more than a younger one, especially if the money is available. An inexperienced traveler will probably spend more than an experienced one.

My data point is like Pete's above--I'm a frugal, fast and light traveler, with a lot of long distance hiking experience. My last XC bike tour was over ten years ago (at age 55), 4400 miles on the ACA Northern Tier route, which cost a surprisingly low $1500, below my $2000 estimate. I probably would have spent nearly that if I'd spent that summer at home.