I'd say you are concerned about a bunch of nothing.
Are you going to do this bike touring thing every month of your life or only once a year....or ...only once?

This is a vacation the likes of which you probably won't have the opportunity to repeat that often. (maybe I'm wrong but I'm assuming you are like the rest of us. )

Why worry about how much food will cost? Take some cooking gear if you want to save money. I'm sure you can figure out how to use it without the solicited advise here. Otherwise, enjoy yourself and eat a lot.
The map will show you the next food source. Plan accordingly.