I've had some luck with Expedia packages. I booked a two bedroom condo for 12 nights, a rental car, and airfare for two roundtrip from Chicago for just under $1200 for early December. They had much shorter stays available, of course. Just like Priceline, you do pay everything up front. With the package I purchased, I can cancel everything EXCEPT the airfare under well disclosed terms, which are quite resonable.

Do read the fine print thoroughly before submitting your payment.
The Lynx buses are another option. If you choose your accomodations on one of the direct bus routes, you will probably have a lot more flexability than with the hotel or paid shuttle options. Go to
http://golynx.com, pick the Schedules and Maps link, then check out routes 50, 56, and the 111 which goes from the airport to Downtown Disney and the Ticket & Transportation Center where you can catch a Disney bus to any park. The website says that a 7 Day pass is $16.00 per person. What a bargain! If you are accustomed to using mass transit, this is a good option.