Paris Hotel Guide(not affiliated in any way with Disneyland Paris) offers a great choice of hotels at a walking distance from RER A access. For example:
The RER: the most direct access to the kingdom of dreams...
From Paris, RER line A takes you fast to the heart of Disneyland® Paris... In just 35 minutes, you can be at the gates of a fairytale land where all your dreams come true! Just get out at the end of the line, Marne la Vallée / Chessy station, 100 metres from the gates of Disneyland® Park.