For the French ones I would use the Logis De France website, you can search by town, just go for the one that's the right price and you fancy. They're usually very local / characterful places which always makes for an interesting experience.
I am just about to do an epic drive from the south west of Portugal to southern Germany with DS (4) and DD (2.5) plus my smelly old dog, I need recommendations for cheap and cheerful B and B is the following 4 areas
GRANADA VALENCIA PERPIGNAN LYON
HELP PLEASE!!!!!! I leave on Monday and have done some googling but it takes for ever and I am running out of time