I've cycled/camped in France for forty-odd years and lived in that country also.
The basic and cheap camping you require is not likely to be found in the Michelin Guide but in a reference that lists all of the most basic sites of which there are thousands. The best and most comprehensive of these is "The Guide Officiel Camping Caravanning" which can be bought in most Bookshops and Supermarkets in France. It can also be bought from the UK' "Caravan Club"and "Camping and Caravanning Club" shops.

The Guide is in French but easily understood using the symbols.
Be advised that all property in France is owned and they do not take kindly to people camping on their land. Do try to learn some basic French even if this is only greetings as the French do tend to be formal about this. I would suggest that the Michel Thomas method would be the most efficient way to do this.

Learn French - Learn to Speak French with The Michel Thomas Method