Try going to
Alamo & National and putting your same dates in, but this time rent the car at the "Disneyworld Car Care Center" (in Orlando) or the "Disneyworld Swan Hotel." Put MCO airport in as your return destination.
I tried this and quickly found a base rate of $160 per week. You'll probably do even better if you use some discount codes available over at Mousavers.com.
Now, obviously, you'll face a bit of a hassle to do this, but the savings are substantial. You'll either have to rent a car at the airport for a single day and drive it to Disneyworld where you will immediately exchange it for the lower priced rental. Or, for better savings, wait a day to turn in your airport rental and exchange for the lower priced car on the next day. This will eliminate the double rental for one day. (You'll pay the high airport rental for 1 day and the lower car care rental for the remaining 8 days.) Your other option would be to take a shuttle from the airport and then take Disney's transportation over to the car care center or the Swan hotel, making your only rental the one at DisneyWorld.
Some little known facts about Alamo/National are that they don't typically charge extra for renting in one location in Orlando and then returning in another location. In addition, when you rent off-airport, you are eliminating all airport concession fees (more $$ savings). Lastly, on congested travel weeks, the costs at the Disneyworld rental locations seems to always be substantially lower than the airport rentals.
Good luck with your search.