If you travel a good bit and rent cars, you're probably aware of the frequent renter programs the major rental companies use. While these can save you money, there are a few ways you can save even more.

Most of the frequent renters programs are free. But some of the companies have higher-level memberships that will cost you. However, Joel Widzer, author of The Penny Pincher's Passport to Luxury Travel, says, "What most people don't realize is that it is often possible to avoid the membership fee by simply writing or calling your car rental company and asking them to waive it. They will do it because the car rental industry is very competitive, and they want your business."

Next, Widzer says to have memberships with at least two different companies. "The first is your primary provider; this is where you will put most of your business so you can earn the highest level of preferential service. The second company is your hedge against regional market variations. As in the hotel industry, rates and availability in the car rental industry can vary from place to place; on occasion, one company's rates will be grossly out of whack. By working two loyalty programs, you won't get caught paying inflated prices..."

When you're looking for the best rate, don't let the company push you into something until you've done all your homework. Don't just look for rates on the Internet. Widzer says, "You have to be persistent, and you have to call the car rental companies directly -- sometimes several times. It is not uncommon to speak with one rental agent and be offered one rate and then call back a few minutes later and get another rate."

And, finally, Widzer offers a word of warning. "Be sure to ask the reservation agent to calculate the total cost of your rental, including fill-up costs if you come back empty. Often the quoted rate leaves out such things as airport fees, city taxes, license fees, and more. These won't sting so much if you know about them in advance."

Renting a car can be an expensive part of your trip. A little legwork up front can save you a lot of money on the back end. It's worth the effort.