France is a camping paradise!
Along the via podiensis, often you can camp for very little money on official campsites, showers and all.
There are countless campsites along the way, some of them only ~5-10€. Many gites allow camping in their garden, too (for much less than a bed would cost, I think I usually paid 5-10€).
I didn't wild camp but met several people who did.
France is very tolerant of it, as long as you do it in a respectful way. If you set up your tent late, for example next to a pilgrim rest area, and leave early, it usually is no problem. No fire, no litter, of course.
In at least one village I even saw a sign on a little patch of grass in the middle of the village that said "bivouac allowed here, from 7pm-7am".
There are also many small chapels along the way where you could sleep under the porch. Often there's a water fountain next to it, sometimes even a compost toilet.
Also, a few "open access" shelters, for example the réfuge de la béate (highly recommend).
So, you have many options.
If you want a list of the chapels, I can send it to you. I got it from a hospitalero in Cahors. Was very useful.
