Take a Long Hike has a sobering post …
… Let’s consider the Appalachian Trail, 2178 miles long. The days of averaging a dollar a mile are long gone, although it can be done. Twenty-three years ago, Roland Mueser, in his later book, Long Distance Hiking–Lessons from the Appalachian Trail, came up with an average cost of $3200.00 dollars or about $1.50 a mile. But that was 1989. …
So what about today? Figure about $2.50 a mile, or $5500.00 for the A.T., and that is conservative. One recent blogger said he wouldn’t feel comfortable unless he had saved $10,000 for the hike. …
Take a Long Hike – Thru-hikes are expensive
Ouch.
besthike.com 
Perhaps I should have mentioned two other things. I’m thinking of a thru-hike that lasts at least five months (I was out there for six when I did the AT in ’03). These numbers also include any travel costs to get to the trail and arrive back home, as well as all equipment and gear. Based on that, today’s average total cost to thru-hike the AT will be around $5500.
An interesting topic. My belief is the range of expenses is so variable as to make the estimated cost, which is based on an average, utterly meaningless.
People like Flyin’ Brian and Skurka maybe spent $1/mile. If a hiker spends their time in motels instead of tents, that cost obviously would go up.
Trail food and equipment is extremely cheap compared with the rest of your life. The cost of a new car is more than a lifetime of equipment. if you own a house your payment dwarfs the replacement socks you might be needing.
If you own neither house nor car, it is far cheaper to travel the world than stay at home and do absolutely nothing. Check it out; it’s true. The author missed the mark; the problem isn’t cost, it’s loss of income.
You make some very interesting points. I almost want to travel the world and test your theory. You are right, however, in that I’d not considered the loss of income. That said, like everything else in this world, thru-hiking costs have risen. The typical thru-hiker that I’m familar with is looking at about $5000., when all is said and done.