Your gateway is CDG, therefore you will be airlinning from CDG or may be sometimes depart directly from an FBO in Paris area BUT the company will arrange transport for you only FROM/TO your gateway. Example, you live in Pontoise; it happens to be there is a flight starting out of pontoise for your day one of the tour, the company will provide you a transport from CDG to Pontoise. If you decide by yourself to go to pontoise directly, when you finish your tour the company will bring you back to CDG NOT pontoise.
Long term car park or RER are the bests options finance wise, otherwise like everyone, that what your 70 euros are for, to cover the enroute journey expenses, that includes Parking, Toll, Fuel, food....
