We've just returned from Disneyland Paris aving paid £14 for 4 adult tickets.
If you go to http://www.raileurope.co.uk/Default.aspx?tabid=2049
and buy any rail ticket they sell you get a free 1 day hopper entrance ticket worth £46.
We chose two stations at random near Paris and had no problem exchanging them at guest services.
The offer lasts until 26th June.