We will be at WDW December 26 to January 5 and the price of rental cars has been insane! We need a full size and for many months it didn't go under $100 a DAY! It's recently gone down to about $55 a day, which I think is still high.
My best suggestion is to check Hotwire.com. I always book through them, and unlike their hotel reservations, you do not pay until you return the car at the end of your trip. You can cancel and rebook numerous times with no penalty. And if you click on "watch this trip" they will email you whenever there is a price decrease. Back in July they emailed me to tell me of a price decrease that only lasted one day. I was able to get our rental car for our Christmas trip for a total of $338 including taxes! Considering it is back around $700 I feel very fortunate.
Just make sure you put in MCO as your pickup place because they also book cars from offsite agencies.