My last cross-US tour ended up costing $25/day, not including travel to and from termini. That included paying for indoor lodging once a week, paid campsites maybe once or twice a week, a handful of warmshowers hosts, and the rest free camping. Food generally cost $15/day, mostly buying groceries.

I went on one five-day trip from home and it only cost $5 total, for one Subway footlong. I carried most of my food from home and received some free meals from new friends along the way.

I met one fellow cyclist who had been out for three years and was spending just over $5000/year to maintain his lifestyle, cycling nearly 8,000 miles per year. He was not a bum, either--good gear, good health, had all his teeth. He was an accomplished freegan.

It's very easy to exceed $100 per day if you want to.