There are car rentals that might cost as much as $300 one weekend, then will be down to just $50 the following week. Such price variations are common in the car rental industry

According to Gary Leff, the founder of the travel deals site viewfromthewing.com, "Car rental prices constantly go up and down in big leaps."

To prevent from booking car rentals that can add hundreds of dollars onto vacation costs, here are some money saving tips for getting the better end of the bargain:

AVOID BOOKING A PREPAID RENTAL

Some car rental companies offer a small discount if you prepay, but Mr. Leff advises not going to do the same because you can no longer save money if rental prices drop before your trip starts, which they usually do.

Upon making your reservation, he suggests going to AutoSlash.com, a site that tracks car rental prices, and adding your reservation details.

The said site will keep track of fluctuations and/or price changes on your rental and also scout competitors' prices.

Users will then get an email when a lower price for the same rental becomes available. By that time, you will have an option to rebook their reservation.

IN ORDER TO SAVE MORE, RENT LONGER

"It is often cheaper to rent for a longer period, because business travelers book shorter rentals and aren't as price sensitive as leisure travelers, who tend to book longer ones," according to Mr. Leff.

"The industry knows this and prices rentals accordingly," he added.

Mr. Leff further said that you must keep the car for the entirety of the rental because agencies can re-price rentals to the higher price if you return it early.

BE OFF-SITE, AVOID RENTING AT AIRPORTS

Rental agencies with airport locations charge a daily airport tax if you pick up your car at the airport.

The airport tax is as much as 25 percent of your entire rental. It is typically more expensive to rent a car from the airport.

Save money by renting with the same company and picking up your car away from the airport.

USE HOTWIRE.COM FOR DISCOUNTS

Hotwire.com offers rentals at up to 50 percent off what renters would pay if they booked with a company directly.

Prepayment is required, and this is the only instance in which Mr. Leff recommends a prepaid rental.

"The downside is that you don't know which company you'll be renting with until you pay, but it will be one of the major brands such as Hertz or Avis," Leff added.

CONSIDER LESS-OBVIOUS BRANDS

While Hertz, Avis, National and Enterprise are popular brands, there are several dozen smaller companies, such as Fox Rent a Car and Payless Car Rental, that often offer rentals at cheaper prices because they're not as well-known.

However, Mr. Leff conveyed the downside of considering less-obvious brands.

"They're usually located farther away from the airport than the bigger brands and may not have a frequent renter loyalty program," Mr. Leff said.

JOIN THE LOYALTY PROGRAM

There's no actual downside to joining a car rental company's loyalty program. It's free, and members receive regular emails with offers like free upgrades and discounted rentals.

Beyond saving money, joining a loyalty program also comes with perks, special offers and they can typically get their pick of cars, making it easier to reserve nicer and newer models.