I've done the "public" transport option a few times and not as bad as it sounds. Four easy steps:
1.The Ryanair bus to Paris takes an hour to hour and a half (depending on traffic) 20 return.
2. Bus drops you in a car park around the corner from Porte Maillot metro stop. Walk to it 5 minutes
3. Get the metro to Charles de Gaulle 1 - 5 minutes (Chateau de Vincennes Direction).
4. Then get the RER A to Marne la Vallee (gates of Disney) 12 return. 30 minutes.
All in should take you less than 2 hours, you'll see a very small bit of Paris and save a bunch of Euros!