There are some huge, very well equipped, teeming and expensive campsites in the Loire Valley. There are also many small and cheap campsites run by the municipality - some in the most delightful places (one at Nazelles Negron near Amboise runs wine tastings and has a pizza van some evenings). We paid around 7-8 euros a night for two of us and a tent, and enjoyed a shady riverbank. There's also one we didn't stay on right next to the chateau at Chenonceau.
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Agreed. Try the one at Sully between the Loire and the Chateau. The same is actually true right across France - excellent simple and cheap camping, very good for transit stops.
Is this your business?