Here's my unbudgeted expense summary of my 2012 thru hike to give those in planning an idea of what it may cost to hike the entire trail and what the money is actually spent on. Those on a limited budget can pick apart areas where they can look to save money. I had all my gear purchased beforehand and am not addressing that here.
Gear $400 - I got lucky that I only had to buy one pair of trailrunners on my hike. I got a replacement pair under warranty and thanks to the wonderful people at The Doyle I got a new pair from the hiker box. The rest of the cost went to fuel canisters, Aqua Mira, tent repair kit and small things picked up at outfitters and for the hell of it I replaced two pairs of shorts, socks, underwear and a short sleeved shirt about 2/3rd of the way through.
Lodging $700 - I spent 32 nights in hostels or hotels(five nights total and only two that I didn't split with another hiker). This came out to about one every four days including 13 zero days in town.
Food (resupply) $975 - spent at Wal-Mart, Dollar General, grocery stores etc
Food (restaurants, bars, delis etc) $1,400 - somewhat surprised by this but understandable. A large pizza and a beer or Coke in each town, not missing any chances to hit up a deli or market within a mile of the trail and taking zeros in town adds up quickly. This could have been a lot higher if I was a drinker. Outside of Gatlinburg and zeros at Trail Days and Daleville I'd have a beer at most in towns. Guessing this accounts for about 1/3 of what I ate on the trail.
Travel $250 - Living in Atlanta helped keep this low. A paid for a few shuttles (back from Trail Days, to bus stop in Medway) a few buses to Bangor and a flight home to Atlanta.
Misc(postage and memory sticks) $75 - mailing home winter gear, mapsand memory sticks (which I bought along the way)
and $700 for side trips to NYC(twice) Boston and DC before getting home.