Check out the Transportation board. There's probably a thread for October and you can see what deals others are finding.
If you find a great deal, book it. Unless you book with "name your price" type of booking service, you can cancel if you find a better deal. (If you do find a better deal, book IT before canceling your original reservation.) Prices may go down closer to your trip, and lots of companies have last minute deals. Generally if you join a frequent renter program you get a 10% discount.
Make sure you allow a little wiggle room in your pick-up/drop-off times. If your flight gets changed and you arrive several hours earlier, you may not be able to pick up your car early. Same if your flight leaves later. But most places will hold your car if you come in a couple of hours later than originally scheduled.
