Is there any ground transportation from the airports to DLR? I didn't see any options when looking at the Disney site even when staying at a resort hotel.
Or you can take a shuttle, like Super Shuttle or Primetime, etc. Which tends to be a little less than the Express. Be sure and enter the name of the hotel, not the zip code, of your destination; it will cost less that way. Otherwise they assume they're picking you up from a private residence. Here's a coupon code, good when you reserve online: http://www.retailmenot.com/view/supershuttle.com
If you are flying into SNA or LGB, and there's 4 or more of you, it might be cheaper to take a taxi; I think they run a flat fee of around $45. Though I don't think you can get the flat fee on the way back.