Lee-I always always always go to
www.carrentals.com. They do a search for you of all the major car rental places and show you the best rates.
Recommendation-reserve a car through them now, and then start checking the prices (I'd check every week); the rental car companies drastically lower their prices on rentals about a week or so ahead of time hoping for some last minute rentals. . If you find the car cheaper, just cancel your old reservation and then make a new one at the lower price. The last several times I've rented a car, I've paid $10-15.