I can tell you how I look for car rental rates. I go to Expedia or Travelocity to see what the going rates are. I start with the cheapest rates and then look for codes for that rental car company. Codes can be found here:
http://www.mousesavers.com/rentalcar.html
http://www.vacationoutlet.com/car/default.asp
http://www.fatwallet.com/t/63/521905/
For instance, I looked up your dates on Expedia and found that Dollar had one of the cheapest rates ($205+ for a full size), so I plugged in code KISS2 (from the Mousesavers link) and got $170 ($223 with taxes).
As for the OP: I also typed in YOUR dates at MCO at Dollar for a Minivan and I got a rate of $199 per week or $251 with taxes.