If you have a chance, don't get the disney express. As long as you don't mind dropping your bags off at the hotel first (which we always do anyway).
We saved about £70-100 by booking the hotel room direct with disney but then booking the train tickets with Eurostar.
Plus theres usually a huge queue when collecting your bags.
One last thing, if your worried about your last day, for about two euros a bag (think it was something like that) you can drop your bags off when you check out and collect them at the station. So, thats basically the disney express but much, much cheaper!
just my opinion and two cents!