6. Compare non-airport rates.
"In general, prices have gotten more expensive at airports," says Taylor. A recent J.D. Power survey found that airport access fees, the surcharge leasing companies pay to operate out of the airport, are usually passed along to consumers.
If you do find it cheaper to rent away from the terminal, don't forget to factor in the cost of getting to and from the offsite agency. If there's no shuttle and you have to grab a cab, it might be cheaper to pay the higher fee.
Also make sure that the away-from-the-airport agency will be open when you want to return the car. A bargain's no bargain if you're standing in front of a closed office on Sunday morning with a car you can't return and a plane that leaves in two hours.
7. Shop the counters.
If you show up at an airport without a rental reservation don't be afraid to go counter to counter comparing deals. "You'll be amazed," says Gillis. "The difference can be up to 50 percent at the same location."
8. Think about where and when you want to return the car.
If you want to leave your car in a place other than where you rented it, you need to include drop-off charges in your shopping, says Gillis. It some cases a higher daily rate that offers lower drop-off fees might be cheaper.
9. Book ahead if you have a special request.
Need a child safety seat or a ski rack? Reserve it at the same time you reserve your car, says Gillis. Ask about extra charges and get it in writing.
10. Ask about mileage.
Some companies include unlimited miles as long as you stay within a certain region. Others cap the mileage. Estimate your needs and shop around.
11. Consider gas and insurance.
These two items can add to the cost of your rental car.
Unless you know you're going to be scrambling when you drop off the car, offer to fill the tank yourself. Otherwise, it's usually a pretty pricey fill-up at the rental office's pump and you can't take any left over with you, says McNaull.
As for insurance, talk to your own agent first. "Be sure you know what your own auto coverages are regarding renting a vehicle," says Abrams. Most customers don't know or understand the rental coverage offered at the counter or how their own insurance will treat a rental car.
12. Never stop bargain shopping.
Haggling doesn't end just because you're at the rental counter, reservation in hand. Gillis recommends you ask if the company will give you any free extras or upgrades. He estimates your chances of getting one are about 25 percent. That's well worth it, he says, "for the three seconds it takes to ask the question."
When McNaull was renting a car in Orlando, the company offered to upgrade him from a midsize to a Jaguar for $12 a day. He declined only because he was traveling on his corporate credit card. "There would have been too much explaining," he says with a laugh.
"Rental car companies want to make money," says McNaull. "But they also want you to be happy so you'll come back. And if you discover the person in front of you is paying 20 to 30 percent less, that doesn't leave you a happy customer."
Dana Dratch is a freelance writer based in Georgia.