If you want to go REAL rural without civilisation skip Germany and the other north countries. Spain is the place, also the climate here is better, you could include Portugal.
Wild camping is forbidden here in Spain, you will find camp spots everywhere, just hide a bit, I do it all the time.
Attractive tourist destinations have higher hotels and hostels prices, if you stay rural you can travel pretty cheap!
If I go from hostal to hostal I google accommodations the night before in google maps, according to where I have my route planed, aprox where I want to cycle/arrive.

P.S. I never have been in Youth Hosteling, no experience with that.