Gasoline in France is near $2/liter, which would be $7.60 per gallon. They usually drive smaller diesel cars which would get 60 mpg on the highway, or better, so it's not that different from driving a Camry here at 35 mpg highway at $3 per gallon. The tolls however are a bite.
Paris to Marseille is 482 miles with $70 in tolls. Still, at 60 mpg, it's 8 gallons of Diesel, which is cheaper there than gasoline, so about $60 in fuel.