The thing is that people vary really widely in their choices. One persons number can be WAY different from another. I will say that your $10-30 range takes in a good bit of the touring community so you are probably on the right track.

I if I had to pick a number I'd say that it is not super hard to get by on $15 a day, that is often what I wind up spending. I am generally not trying to get by as cheap as I can though. I have heard that folks have managed on $5, but that seems like a very big stretch and I wouldn't even consider going if I didn't have at least $10 per day available.

There are a few things that can run the number up a good bit. Sport drinks and soft drinks add up fast if you drink them. Alcohol even more so if you drink that. Another thing to consider is that part of experiencing an area is eating the local cuisine. It would be a big shame to ride the ST and not eat a good bit TexMex, Barbecue, Cajun food, and gulf seafood.

What ever you decide, it is smart to have more money and time available than you need. Restrictive budgets and schedules can suck much of the joy out of a trip. If I thought I needed $15 a day I'd make sure I had at least $20 per day available.