If you're touring the US, I'd guess $20/day for camping; $10 for food; $100/week for a hotel or motel room; $200 a month for incidentals. If you toured Southeast Asia or China and stayed in hotels the whole time (camping is rarely done there btw), it'd probably cost you half.
However, there are some places in the US where camping is more affordable. For example, the hiker/biker sites in California are $5 or less a night, and don't require reservations. I believe that type of setup is common on the West Coast.
My only recommendation is not to go
too crazy with saving money. It's good to be prudent, but at a certain indefinable point you go from "making your dollar stretch" to "obsessively counting your pennies" (aka "budgetitis"). It happens a lot to backpackers, who even get a competitive streak about who can spend the least. It's better to spend a little less time on the road and not worry about money, than to spend an extra week or two and get a knot in your stomach when a candy bar costs $0.95 instead of $0.75.
