We have been all over France, on various campsites (staying in mobile homes).
Our favourite has been Gascony: Great beaches, large lakes, good cycle paths through endless forests, mountains (we had a day trip involving cable cars, ski lifts etc in August).
Going to the Vendee this yr - 12 nights in AUGUST in site walkable to beach, P&O Fastcraft Portsmouth/Cherbourg crossing with bikes on roof - for under £1000 including insurance. Should be a 4 hour drive from port - Gascony was a 2 day stint.
We also like the Languedoc as on the Med - again a 2 day drive.