2. Always rent the smallest car

The smallest cars have the cheapest rates, and if the location doesn't have a subcompact when you arrive, they'll give you a free upgrade to the next smallest vehicle they have on the lot. The people who deliver cars to satellite locations (called shuttlers) don't like squeezing into subcompacts any more than you do, so they don't stock the lot with small cars unless they have to. In locations with very few cars, you will often--as a result--be given a full-size car for the price of a subcompact. And if they do have a subcompact, and you want a bigger car, you can always ask for an upgrade on the spot, but there's no reason not to try for the lower rate. This strategy surely won't work at a giant airport like Miami's, where there are hundreds of cars (and therefore dozens of subcompacts) on hand. But it will work in downtown locations and smaller airports with room for only a few cars.

The following illustrated examples speak for themselves, and give a glimpse of the savings at a given moment in time.

3. Compare rates between downtown and airport locations

Say you're arriving in St. Louis and need a car for four days. If you rent one (a subcompact, naturally) from Budget's airport location, you'll pay $51.99 a day, or a total of $207.96. But if you rent the same car from Budget's downtown location, just a few blocks from the convention center, you'll pay $39.99 a day, or a total of $159.96. And here's the best part: You get the lower rate--a savings of $48--even if you return the car to the airport. But, you may ask, doesn't it cost something to get from the airport to downtown? Yes--all of $3.50. That's the price of a Metrolink ride from the airport to downtown.

4. In New York, the savings can be even greater if you're willing to take a train ride to the suburbs

Say you want to rent a car for this Fourth of July. At any of Hertz's Manhattan locations, a subcompact will cost $71.99 per day. But if you take a train to Hertz's location in North White Plains, the same car rents for $42.99. The rental lot is right next to the train station, and the ride takes no more than 50 minutes from Grand Central Station ($7 one-way). The savings are even greater if you keep the car for a week: $311.99 at North White Plains, compared to $409.99 in Manhattan. What's more, you still get the lower rate even if you return the car in Manhattan.

5. Check differences between weekend and weekday rates

Sometimes you can save money by keeping the car longer. At airports and other locations catering to business travelers, weekend rates are so much cheaper that it might make sense to pick up a car on a Saturday or Sunday. (At some locations, there may even be more than one rate on the same day!) For example, at the Dallas-Fort Worth Airport, National charges $55.99 a day for a rental starting on a Monday. If you keep the car for three days and return it Wednesday night, you pay $167.97. But if you pick up that same car on Saturday night and keep it for four days, you pay for two days at the weekend rate of $21.99/day and two days at the rate of $48.99/day, for a total of $141.96. Voila! A savings of $26.01! If you pick up the car Friday night, you pay only $163.95, still $4 less than what you'd pay to pick it up on Monday morning, and you get the use of a car all weekend.

In Manhattan, where car-less urbanites flee the city on weekends, the equation is just the opposite. Weekday rates are lower than weekend rates, but again, you can save money by keeping the car longer. For example, if you pick up an economy car at any of Budget's Manhattan locations on a Friday and return it Sunday you'd pay around $75.99 a day, or a total of $227.97. But if you pick up the car the night before (Thursday) and return it at the same time, you pay only $65.99 per day, or a total of $197.97. That's a savings of $30, which will more than offset the cost of storing the car overnight in an expensive Manhattan garage if you can't find a parking spot. Why do the car rental companies do this? For the same reason restaurants have early-bird specials. They want you out before the big rush. If you take a car off their hands on Thursday night, that opens up room for one more car they can rent on Friday.

6. If you're keeping the car for four or more days, check if there's a weekly rate that might be cheaper Weekly rates for most car rentals usually kick in on the fifth day.

Most rental companies' weekly rates allow you to keep the car for five, six, or seven days with no difference in price. In many cases, the weekly rate might be cheaper than the four-day rate, and in a few cases, even cheaper than a three-day rental. Here's an example of the latter: If you pick up a subcompact car from Alamo at the Charlotte, North Carolina, airport and keep it for three days, you'll pay $60.99 a day, or a total of $182.97. Keep it for four days and you'll pay $243.06. But keep it for five days (or pick it up a day earlier) and the weekly rate of $146.99 kicks in, a savings of nearly $100.