Hi Roisin,
It'll be more economical to purchase
Billet Ile-de-France tickets for your trip from
CDG Airport to Paris (which includes transfers to any Metro station within Paris, such as Dugommier) and also from any Metro station in
Paris to Disneyland at Marne La Vallée station.
Keep in mind that
Billet Ile-de-France tickets are good for the Metro as well as the RER. For example, when you buy your
Billet Ile-de-France from CDG Airport, use it for boarding the RER B to Paris, get off at Chatelet Les Halles, transfer to Metro Line 14, direction Olympiades
using the same ticket, until station Bercy, transfer to Metro Line 6, direction Nation, one station until Dugommier.
This also applies to your trip from Dugommier Metro station out to Euro Disney, which is the last stop on the
RER A line, direction Marne La Vallée. Enter the Dugommier Metro station, go to the ticket window and say "Disneyland" and the ticket seller will likely ask "aller-retour?" (return tickets, which are two one-way tickets). Then, you use these tickets for the entire
Paris to Disneyland train trip : Metro Line 6 direction Etoile till Bercy station, then Metro Line 14 direction Gare St. Lazare till Gare de Lyon, then transfer to the RER A direction Marne La Vallée, all using the same
Billet Ile-de-France.
If you plan on doing a whirlwind tour of Paris one day, hopping on and off the
Metro, Buses, etc., think about purchasing a 1-2 zone Ticket Mobilis, (about 5,80€) which is a day ticket good for unlimited rides until the end of service (12:45 AM).
Think about using
Google Street View to see
Dugommier station and it's surroundings. It'll help you find your way to your hotel close by.
Best regards,
Ben