That is a myth and lots of French people a couple of years ago were quite peeved about it until they realised it wasn't true. No way would the private co-operate with the government. One of the ways they get so many people using the motorways is that you can do 160km per hour on a good stretch of road notably the A16 from Boulogne down towards Paris (very few lorries use this motorway, preferring the A1).
As for the price of the tolls, all depends on the company who owns them. Some are more expensive than others. Take for example the bridge from the mainland over to Noimoutier; once the tolls paid for the bridge it's now free.