Anne if you are going to the Tarn, a good stopover after Loire is Menat, it is 154 miles from Orleans and 171 from Millau. We paid €9.5 + tax with a 10 amp ehu. It is on the river La Sioule and has a grassy beach.
If you want to stay longer it is close to Puy de Dome and the whole volcanic tourist industry.
We are going to splash out and stay here Beaugency. It is right on the Loire a Velo path on the Loire near Orleans, but is expensive, €15.05 per night. ( I thought I would treat my wife)
Don't forget to leave a review of the French and other European campsites you have visited!