It really does depend on how you want to hike and how often you go into towns. If you try a traditional AT type hike with lots of days off in towns, you are going to spend a lot. If you stay out of towns, then you can do it for less. Also, how long you are on the trail will impact this a lot.
However, I found in 2003 that I was spending roughly $8 a day in food on the trail. For stop in town with no night stay, I’d spend another $20 in eats and treats and such. If I spent the night, it would jack up to more like $50. A zero day would cost me around $70. Some places are high cost, like VVR, where I dropped $105 (about standard, and totally worth it although I’m told in 2004 they had a new chef).
Suge