Look for deals on websites such as Travelocity and Expedia. Contact the cheapest companies directly online or by phone. Then call the specific location to negotiate the cheapest rate.
They include Ace Rent a Car, Pay Less, and Midway, which you can find at www.carrentalexpress.com or www.carrentals.com. Also consider shopping at www.hotwire.com, a discount-travel site that offers deals without revealing the name of the rental agency until booking is completed.
They're generally available to members of AAA, AARP, Costco, Sam's Club, labor unions, professional associations, and other groups.