The RER is often an experience of watching for pick pockets or even skirmishes. Always keep your valuables (especially your passport) on your body not in purses or pockets.
There are indeed frequent buses (350/351/well hidden #93 to the end of Bobigny Metro line 5) from CDG terminal 3 Roissypole bus depot (between 1 and 2, next to IBIS hotel) to various parts of Paris, but they can take a while (an hour and a half or more), especially if there is traffic (most all day!). The fares are MUCH less than the RER (2-3 t+ tickets/3-5 euro vs almost 10 euro), and they avoid many of the stairs and escalators to the RER, and most of the pick pockets! Metro Line 5 (some stairs) is an easy 20 minutes into the city with Gare du Nord & Gare de Est stops.
BONUS: Because the buses/metro use different ticket machines than RER, those machines DO work with many credit cards - maybe even mag stripe ones! Machines inside in the same terminal.
Here's a 2013 detailed article on how I have gotten in/out of CDG-Paris in the past (:
http://www.frugaltravelguy.com/2013/...e-visitor.html
"Tip 10: How to travel between Paris and CDG for 3.20 EUR
My final tip is how to travel between Paris and CDG for 3.20 EUR. No one I spoke with in Paris knew about this option including a Comfort Hotel Bobigny receptionist—and he, of all people, should have!
On arrival at CDG, get to the Terminal One. Then take the bus #93 to Bobigny Pablo Picasso Metro station. The ride should take about 30 minutes.
Bobigny Pablo Picasso is served by Line 5. That means that unless your hotel is in the vicinity of the Bastille, you will need to transfer to another train (if you do stay in central Paris, that is). The ride to the Grands Boulevards, for example, will take you about 40-45 minutes with one change of trains. Just remember the caveat about luggage and general lack of elevators, though."
It departs from Terminal 3 Roissypole bus depot (not terminal one) It's a lot faster and more consistent because it is outside the traffic areas than #350 or #351 and cheaper (vs 6 euros) because the bus terminates at the end of the metro line so only 2 t+ tickets needed to downtown Paris. It leaves once per hour mostly on the hour and can get you into Paris in about an hour or a bit longer reliably. It is also a more comfortable bus than 350/351 and seems to have more locals.
http://air-travel.discoverfrance.net/cdg_info.shtml
http://www.keolis-cif.com/fileadmin/...s_ligne_93.pdf contains the schedules and route.
Get a book of 10 (carnet) metro tickets for a significant discount price.