It gets costly at the counter

Heading home for the holidays can come with a hefty price tag.

Although gas prices are the lowest they've been in years, if you're renting a car, increased demand during the season means you'll likely encounter higher prices - especially if you haven't already locked in a rate.

And that's not counting the extras rental companies try to get you to sign up for.

"The key is what happens at the counter," said Philip Reed, senior consumer advice editor, at Edmunds.com. "Know they're seeing you as someone who can be sold additional products."

Here are four tips to help you save money:

1. AVOID THE AIRPORT

Reserving a car well in advance of holiday travel is one of the best ways to lock in a cheaper rate. But failing that, you can often find less expensive rates at car rental locations that are not at an airport.

This could be tough, particularly if you're flying into your destination. But it can be worth seeking one.

"It's safe to say that in most cases, airport locations are going to be more expensive," Reed said.

2. SKIP THE EXTRAS

Expect a barrage of sales pitches once you hit the rental counter and are ready to start your vacation. Do you really need GPS navigation or satellite radio? If you have a smartphone it likely has apps that provide similar functions for free.

Another common extra is an automatic toll collection device. They can cost about $5 a day and will save you time at busy toll plazas. But if you're not likely to see many tolls on your trip? Skip it.

Also consider the full costs of upgrading to a larger car.

Often rental agents will offer a vehicle upgrade, couching it as an increase of just a few dollars above the original daily rate. But that can add up, particularly on trips of a week or more. And bigger vehicles generally equal more money at the pump.

3. UNDERSTAND INSURANCE OPTIONS

The most costly extra that car rental agents will try to sell you is a collision damage waiver, which offers protection from theft, vandalism or other damage.

It's also a major source of revenue for car rental companies, easily amounting to an extra $20 or more a day on top of what you're already paying. Generally, buying this type of coverage is unnecessary.

If you own a car, your personal insurance policy likely covers rental cars. It probably also extends liability insurance to your rental, though you should check ahead of time with your insurer. In an accident, liability insurance typically pays for the cost of damage to the other car or its passengers' injuries if you're at fault.

If you're charging your rental on a credit card, you're probably covered in case the car is damaged or stolen. But liability insurance may not be included.

The four major credit card payment processors - Visa, MasterCard, Discover Financial Services and American Express - offer some form of rental car insurance coverage.

Most only cover what your personal insurance does not, this is also known as secondary insurance. And cards have plenty of exclusions.

For example, Visa's coverage tops out at 31 days if you're renting a car outside your country of residence. In the U.S., though, it only covers a 15-day rental. And not all MasterCard credit cards offer coverage on rental cars, said Jill Gonzalez, spokeswoman for credit card tracker CardHub.

Remember, you must book and pay for the entire rental car transaction on the credit card for the coverage to apply. You also must decline the supplemental insurance and collision damage waivers offered by the rental company.

In addition, keep in mind that this type of rental car coverage typically doesn't apply to debit cards.

4. FILL THE TANK YOURSELF

Most companies require drivers to return the car with the gas tank filled to the same level it was at the start of the rental period. If not, they'll charge you for the shortfall, and at generally higher rates than you'd get at the pump.

They also may suggest you prepay for a full tank of gas so that you won't need to worry about filling the tank upon your return.

"This is something that should definitely be declined," Reed said. "The only way to profit from it is if you coast into the rental return lane, otherwise you're giving them whatever is left in the tank."