There are a few websites where you can look for hostels, I don't know about anything specific for Disneyland Paris, but in any case that's only about an hour away from central Paris with the RER A. You could take a look at hostels at
www.hostelworld.com. However in Paris hostels are usually expensive, so I would recommend you to look for a cheap hotel rather than a hostel. You could use
http://www.hrs.com/. Or you could
search here in TT for Paris Hotel and take a look at the thread that deals with hotels and hostels in Paris.
In
expedia.com you can find some decent prices for hotels which are only a few minutes from Disney Paris.