I do intra-Florida one-way car rentals about 6 to 12 times annually. As
FCDub notes, pricing is indeed unpredictable. It just depends upon where each rental firm needs cars. I've had rates as low as $5.95/day. Other times, it can be close to $100/day.
You really do just need to spend some time checking rates. Just make sure you don't pre-pay anything. Then, continue checking rates as your trip approaches. You can modify the reservation if the price drops.
Edit: I didn't read the first post correctly. I see that you weren't talking about one-way rentals. That said, the concept of checking various pick-up/drop-off locations applies.
That said, if you're not needing the car while you are in Orlando, you can experiment with two one-way rentals. Depending on the length of your stay, two one-way rentals might be cheaper. Plus, you wouldn't have to pay the nightly parking fee.
Alamo/National has locations on Disney World property (Car Care Center, Hilton Buena Vista Palace across from Disney Springs, and the Walt Disney World Dolphin).
Avis, Dollar,
Budget, and Hertz can be found at the various Disney Springs Hotels (all within walking distance of Disney Springs).