Go to autoslash.com. They do the shopping for you. You can shop for rental deals from Advantage, Dollar, Thrifty, Hertz, and a few others. The only disadvantage I see so far: You need to setup a ressie for each company that you wish to shop. I have 4 separate ressies setup for my Hawaii trip in March (Advantage, Dollar, Thrifty, Hertz).
In fact, I just got an email showing they found a better deal, cancelled the previous deal, and reserved a new deal....and I didn't have to lift a finger.
The newest deal for a 9-day econ. car: $321 or $36/day (that includes everything...taxes, fees, rental surcharge {which is crazy expensive...even for HI}, and etc). $321 isn't bad for HI prices but March is several more weeks away...I'm sure more deals will come.