Early AM transport to CDG

There are two options ... a shuttle (paris-shuttle) or a taxi. If it were me,I would book a room at an Ibis hotel at the airport (there are two) for my last night in Paris. If you book far enough ahead you can get quite a low rate, perhaps lower than your hotel in the Marais.

You didn't screw up. You'll get home in time for a stale baloney sandwich at lunch - - how's that for pinching pennies? Norma's a big spender (loaded from a wealthy family). This thing: http://www.accorhotels.com/gb/booking/hotels-list.shtml lists her Ibis's and others on the airport in the Accor chain. If you fiddle with the whole list you'll find an ETAP and an F1 which are a lot cheaper. The rooms on these two are identical, except that there's only a sink in the room of the F1. Both are served by a shuttle that leaves a zillion times an hour and will have you at the terminal in ten minutes or so. No matter what transportation you use, if you leave the Marais at four you'll probably miss the flight.

The Etap and Formule 1 hotels that are closest to CDG are the ETAP HOTEL Roissy CDG Paris nord 2 and the hotelF1 Roissy Aéroport CDG PN 2 hotel. They're located right next to each other and are served by the free Accor shuttle bus mentioned by Ed. The only problem is that the first shuttle doesn't depart until 05:15. There is only one Ibis hotel that is located right at the airport. It is the Ibis Paris CDG Airport hotel. It's next to Terminal 3 and close by the CDG 1 RER station and the free 24/7 CDGVAL driverless shuttle train that connects all the terminals. The next closest Ibis hotel is in the same location as the Etap and Formule 1 hotels listed above and is served by the same Accor shuttle bus. You could spend your last evening in Paris, take a late RER B train to the CDG 1 station. and walk to the airport Ibis hotel. In the morning you can take the CDGVAL to your departure terminal any time you wish. For a flight across the Atlantic it's wise to be at CDG three hours before your departure time. However, you probably could cut it a little closer for an early morning departure. (But I'm not advising you to do that.)

I second Tim's idea of staying at the Ibis in the airport. That way you rely only on yourself to get the shuttle train and belly up to the check in counter on time. You might be too early for Ibis's good breakfast but you can get something to eat at the airport after you check in.