I have never had any (real) trouble finding a place to sleep while
touring through anywhere in Europe the way you are planning. The towns
are close enough together that if the hotel is full (or there is no
hotel), 10-20 miles down the road there probably will be. I think
finding something for $30 or less might be hard though. It seems that
each town has someone that will take you in like a bed & breakfast, if
you ask around. I learned in Italy that asking the town police was a
good idea for finding these people who rent rooms now and then.

It's really the most fun way to go.

-Gary