I'm traveling about the same time you are and I'm looking at renting a car for the frist time ever so I will share with you what I found.
First check out
http://www.mousesavers.com/rentalcar.html
I'm traveling during a similar time to you (Sept 24-Oct 6) and I just wanted to rent a car for a few days, but it is cheaper for me to rent it for a week. I found out that it is more expensive to rent at MCO and return it to somewhere other than there. So I decided that I would rent a car from National either at the Car Car Center (by the MK) or the Dolphin Hotel. Here are the rates I got for a 1 week rental using the priceless code (Contract ID 6600330) and the entertainment coupon (Coupon ID 10009123). Also if you have not already purchased the emerald asile membership there is a link for a free one on the mousesavers page for National.
Intermediate Car Sept 25-Oct 2 (Pick up Dolphin Resort)
1 week 161.59
Less $20.00 entertainment coupon
subtotal $141.59
Fl surcharge/2.05 day fee 14.35
license recoupment 3.43
State Tax 10.36
Total $169.73
Intermediate Car Sept 25-Oct 2 (Pick up WD Car Care Center)
1 week 161.59
Less $20.00 entertainment coupon
subtotal $141.59
Miscellaneous Srvice charge for $2.00
Fl surcharge/2.05 day fee 14.35
license recoupment 3.43
State Tax 10.36
Total $171.73
If you do not need the car at the airport take the Magical Express to your resort and then rent the car (you will not be charged the drop off fee then). Also from what I have learned you can check rates constantly and book a new reservation and then cancel the old one with no penalty.
Hope That Helps Some
