Try checking out Mousesavers.
Also, if you have a Costco card, you can go on their website, then click Travel at the top, and try their car rental discounts.
I got a midsize (Emerald Aisle) from National for a week spring break (March 14th to 20th) for $203 total including taxes. I used the code from Costco combined with National's $30 off a week coupon on National's website.
I prefer National as you just go pick out you car, load it up and stop at the exit to go. It is so quick. I've had to wait in a long line in Alamo (years ago, now they have a quick service as well).
This was about the best we could get, I'd love to get better and may try Priceline the day before we travel. I love convenience, but saving money is better! I've gotten a car for $10 in St. Louis with priceline before, so we'll see. I've used them for hotels and rental cars in St. Louis and been very pleased!
*** Just saw, you are talking Disneyworld in Orlando or
Disneyland? ***