Hi Kelly!
I am getting really excited for the Dopey Challenge!  We are counting down the days and ramping up the miles in this house:)
There are still plenty of rooms available on Walt Disney World Resort property.  You can book them 
online, or by calling 407-WDW-IRUN.  There are rooms in all price categories.
You could also stay off-property, but I highly recommend staying at a Disney World Resort.  Guests at the Disney Resorts will have access to runDisney buses that will take you to and from all race weekend events.  This is a huge convenience, especially if you are doing the Dopey Challenge and will be racing four mornings in a row.  Otherwise, you will have to fight the traffic coming in.  The buses will also take you to and from the expo for packet pick-up and any other events you sign up for (Pasta parties, etc.)
I have stayed off property before, so if you do choose to do that, just be sure to leave your resort by 3 a.m. on the mornings of the half and full marathons.  Traffic gets backed up early, and you don't want to have to worry about being late!
I hope this helps!  Please let me know if you have any other questions.