My trip last summer, NH to St. Louis round was more expensive than it should have been simply because I didn't have the camping gear I was hoping to be set up with before the trip. As a result I had no camping stove with me. Also I didn't have a sleeping bag(mid-August-mid September trip). The lack of a sleeping bag tossed me into a hotel room two of the four nights I spent in a hotel. I knew what I had for sleeping clothes would get me easily down to 50 degrees but I knew I didn't trust it any lower than that. 2 nights of the trip had temps forecasted down in the low to mid 40s, I bailed and headed for a hotel room for safety. Another night I was recovering from a rather abrupt case of stomach flu and pretty much took a short 24 mile day and grabbed a hotel to see if i could get enough of a recovery to make good ground the next day(ended up with 146 miles the next day). The fourth night was simply getting into town with rain for the past 45-60 minutes and it was already after dark and I didn't have a campsite found yet and I said the heck with it and went straight the hotel. The trip was 2600 miles in 22 days. I the first leg of the trip(742 miles) I was pretty much eating on bike style food only. The remaining trip I ended up eating out pretty much everynight for supper and then again for breakfast.

Total cost: $501.08
4 nights in the hotel: $239.18
Average cost per day: $19.29

If I would have had the sleeping bag and the stove my cost would have been significantly lower. I could easily see being able to get it down to under $5 a day, quite easily. That's stateside cost. You get someplace outside the US it could be even cheaper...at least once your there.