From either of the two main Paris airports, The RER line “B” connects you to the Greater Paris transport system.
From Charles de Gaulle Airport, a free airport shuttle will take you to the RER station. (Note: Going into the airport from Paris, there are two RER stations at CDG Airport: The Paris CDG-I stop and the Paris CDG-II stop. Check or ask which stop services your airline. There is usually a list of airlines inside the train car). A sample RER trip to Paris center costs €8.70 (€6.10 for children 4 to 10 years old or eligible reduced fare recipients).
From Paris-Orly Airport, the Orlyval automatic metro will take you to the AntonyRER connection for €8.30 (€4.15 for kids). The Orly to Paris ride costs €10.75 (€5.35 for kids).
RER fares vary because they are based on distance traveled and “zone fares” crossed. I’ll further explain “zones” below. Either way, this is comparatively, still some of the cheapest (and fastest) Paris transport options.
RER tickets can be purchased like metro tickets, cash or charge, and either from the ticket window or from machines with the sign saying “Billetterie Automatique”.
When you purchase a RER ticket, you have to specify your destination, and getting the appropriate ticket is important. So, until you are more familiar with Paris transport, it would probably be easier to buy from the ticket window attendant. Most of them speak at least rudimentary English and as long as you can indicate where you want to go, they’ll get you the proper ticket.
The Paris bus network is extensive and readily available from the moment you arrive at either airport. Special bus lines will connect you with the whole of Paris transport.
From Orly Airport, take the Orlybus (€6.90) direct between Orly and Place Denfert(30 min. trip), or you can take local service lines 183, 285, 292 (cheap single ticket fare).
From Charles de Gaulle Airport, take Roissybus (€10.00) direct to Opera, or take local service line 350 or line 351 (€5.10).
At these prices, I know there isn’t anything cheaper, short of getting a ride from your Auntie.
The 350 bus links Charles de Gaulle Airport with Paris at the Gare de l'Est rail station.
The 351 bus links Charles de Gaulle Airport with Paris at Nation.
Stops for the 350 and 351 buses are:
Charles de Gaulle Terminals 2A, 2C, 2E-2F, 2D, 2B and 1.
There is a 15 minute free shuttle ride (N2) linking Terminal 2G and terminal 2C (entrance 4).
Don’t be too pressed for time as bus trips can sometimes reach or largely exceed the hour mark, especially if traffic is uncooperative.
The Noctilien bus service operates at night from 00:30 am to 5:30 am, with 45 lines and 5 very central hubs: Châtelet, plus 4 railway stations in the heart of Paris:Gare de l’Est, Gare de Lyon, Gare Saint Lazare and Gare Montparnasse.
Wait time varies from 10 minutes at the busiest stops in Central Paris to an hour in the most remote locations.
The Noctilien basically costs €1.50 per "zone" traveled. You can use a Metro ticket, or buy a ticket -but not a book of tickets (carnet)- from the driver. A second or additional ticket(s) may be required depending on whether you’re going out of Paris city or need to change buses, etc.
Find the bus lines you need for day or night service, including night buses to Orly or Charles de Gaulle Airports by going here. (You may have to click on Rechercher son parcours, then click on the map).
You can figure out your itinerary via public transport for any 2 points in Paris by clicking here.