If you're struggling to keep up with rising mortgage payments and record gas prices, here's a way to save hundreds of dollars a month:

Downsize your ride.

You'll give up surprisingly little switching to a smaller car or sport-utility vehicle.

But you can cut your monthly payments in half if you're spending $500, $600 or more to drive a luxury sedan, big SUV or full-size pickup and pay less on gas and insurance.

Just look how quickly the savings add up:

Lower monthly payments: $250. Let's say you borrowed $30,000 for 60 months at 7% interest. You're paying about $600 a month. Reduce that to $18,000 for 60 months and you'll pay $350.

Less costly fill-ups: $100. Drive 1,000 miles a month and average 15 miles per gallon, you'll spend $250 a month on gas at $3.75 a gallon. Drive the same 1,000 miles but average 25 m.p.g. and you'll spend $150.

Reduced insurance premiums: $10. The experts we spoke with say you can save 10% to 20%. That means your premiums could drop from $600 to $480 a year for the same coverage.

Total monthly savings: $360.

That's far more than anyone can save by scrimping on things like eating out or going to the movies.

You could cut your costs even more if your current vehicle is out of warranty and you buy a new one or a late-model used car or truck that's still covered by a factory guarantee.

Not having to worry about unexpected repair bills is a big plus, and many 2008 and 2009 cars and trucks are backed with the best warranties we've ever seen.

Of course, there's a trade-off to downsizing your ride -- you'll be getting around in a smaller, less powerful car or truck.

But smaller doesn't mean cramped. And less powerful doesn't mean the best small cars, compact cars, compact wagons and small SUVs aren't a blast to drive.

We think you'll be surprised at how much fun they are, and how much stuff you can pack into them.

Many people buy a large pickup or SUV for tasks they only do once in a great while, like hauling furniture or tackling a muddy, rural road. But they're paying a lot for capabilities they use very little.

Think how much easier it would be to park a smaller SUV at the grocery store or mall. And that's something you do every day.

The biggest hurdle to downsizing your ride will be financial.

Edmunds.com says one out of every four auto loans are "upside down," which means the borrower owes more than the car is worth.

That makes it hard to get rid of a costly car or truck without spending thousands of dollars in cash to make up the difference.

The average deficit has grown to $4,300 as the resale value for large pickups and SUVs -- the best candidates for downsizing -- has slumped.

If the difference is less than $2,000, you could still save money by downsizing, even if you must borrow money using a home equity line of credit or your credit cards. (Editor's note: This is a very rare exception to our rule against taking cash advances on your credit cards.)

Another way to escape an upside-down loan is to buy a new car or truck with a rebate that's large enough to make up the difference. Unfortunately, the biggest rebates are on the biggest pickups and SUVs.

But we've seen cash-back deals of $3,000 or more on sporty cars like the Pontiac G6 and Vibe. So look around. These links will show you all the rebates and discount financing deals as they're announced, for all major brands.

Getting out of a costly lease can be a little trickier.

Sometimes dealers can help you turn a car or truck in early, without paying the big penalties called for in your contract.

If not, a new type of Web site can help you transfer your lease, including the monthly payments, to another consumer.

Finally, here's one way not to reduce your car payments -- 7-year loans.

You'll almost certainly regret stretching your payments out that long. Take a look at our 6 reasons to avoid extra-long auto loans.

By Regan Doherty

Interest.com Associate Editor

Have a question about cars or your finances? Ask us at editors@interest.com.