It really depends where in France. Many inland aires can be free, but coastal aires charge.
If you intend to eat out, it can be expensive, we very rarely eat out in France, except maybe for Plat d Jour (meal of the day at lunch time) This can be good value, or use a truckers Routier!
Lidl is cheap same as here and beer and wine is cheap in supermarkets, but buy a pint in a bar and you will pay!
The cheapest are bars which sell the lottery tickets and gambling, sorry the name of them has just slipped me!
Use the RN roads, follow rivers and you will find nice places!
Just remembered PMU bars! (Cafe PMU)