Also try going through the rental companies website. You can usually get the trucks cheaper off airport rental. Like Hilltop I have been using Enterprise and rented a 4 door 4 wheel drive dodge last year. This year I reserved the same thing from Enterprise and have t reserved for 18 days at 608 dollars. There are 3 locations around and two of them where double that cost.
Another nice thing is you can reserve the truck without any down payment. This way you can continue to look for better deals or cancel if something comes up.