Last year we went in September. Rates were really high the months before the trip, I think I booked a intermediate for 250 for the 9 days on National or Alamo. Then as the trip got about a month away Alamo came down to 197 w/ the costco code. I checked mousesavers and just tried every car code and agency I could. The September before we rented for 130 for 9 days, rates went up last year as fleets got smaller. We have rented from Alamo and National and like them the best, but Dollar was also good. Hotwire about a month out is also a good bet, all of their car companies are in the airport.