We never used to pay or camping areas in France. There are plenty of free areas, many of which provide services (emptying, water) across the country and it is important not to forget that legally a camper has the same rights as a car parking, As you follow the statutory period of up to seven days on a single site, sometimes 24 or 48 hours.
There is everything a page dedicated to this issue : Park in France.
You can find internet sites listing services and parking areas as AireCampingCar. We use mobile site park4night, rather well !