You will find that Orbitz and PriceLine have some last minute deals on rooms. There are specific ways to search for a Disney Resort. This involves searching for free parking, free wifi and most most important, no convenience or resort fees. But this is subject to availability. and kind of semi last minute. You don't know which resort you actually get. With these, you pay in advance for the whole stay. Never done it, so no idea about refunds/cancellations. Note also that if you add kids, you may be charged the extra adult fee. They treat children just like adults. You can sometimes book two and then add the children by calling Disney.
As others mentioned, there are some travel agencies that have special group rates. From what I know, they will require payment in full 30 days prior to arrival, but refunds are similar to room only (I think it was up to 5 days prior to arrival) You can add tickets but no dining plan.
All these are room only offers BTW. With some of the TAs you can add tickets, but you would be better off getting them from
UT in any case.