Cycle touring is a expensive way to cover territory relative to motor transport. Thus a sort of obsession on how to do it 'cheaply.' I can travel 50 miles in my car for about $5 in fuel cost. I can pedal 50 miles on the fuel in a jar of peanut butter(3000 cal/16 oz)for about the cost of the gasoline. Of course, I'm not likely to fuel myself with just peanut butter, so the cost of 3000 cals is going to be significantly higher than the cost of gasoline for equivalent mileage.
In the car, I can cover 10 times the distance in a day than I can on my bicycle. That means 10 overnight stays vs 1, with the attendant cost, unless wild/stealth camping all the time. Thus the necessity for frugality with overnighting expenditures.
Add to this all the misc cost like batteries, entry fees to whatever, bike repairs, souveniers, feel good snacks, etc.
$25-100/day for reasonably comfortable touring, depending on your definition, minus the cost of staying home. Probably net of about $15 for the basics.