If you think cars are getting too expensive, you may be right. A new report shows that the average price of a new vehicle is out of reach for people in medium-income households in all but one of the 25 largest metro areas in the U.S.

The report by Interest.com shows that Washington, D.C. is the only American metropolitan area in which a family earning the city's median income can afford the average price of a new vehicle, which was $32,086 in 2013, according to Kelley Blue Book. That price equates to a monthly payment of $633, assuming the buyers put 20 percent down, financed for 48 months and principal, interest and insurance did not exceed ten percent of the household's gross income.

Average-earning residents of Washington, D.C., can afford to pay $32,531, or $641 per month, for a vehicle. The rest of the nation can afford significantly less. Simply put, people are spending far too much money on their cars.

"Too many families are spending way too much on new cars and trucks," said Mike Sante, managing editor of Interest.com. "Just because you can manage the monthly payment doesn't mean you should let a $30,000 or $40,000 ride gobble up such a huge share of your paycheck."

After Washington D.C., residents of the San Francisco and Boston metro areas were found to be able to pay more for a new car, based on median income, but it still wasn't enough for the average vehicle. Here's how much Interest.com says the average-earning car buyer can afford to spend on a new car in seven major metro areas:

- New York City: $21,907 affordable purchase price/$441 maximum monthly payment

- Los Angeles: $20,637 affordable purchase price/$416 maximum monthly payment

- Chicago: $21,409 affordable purchase price/$434 maximum monthly payment

- San Francisco: $28,009 affordable purchase price/$563 maximum monthly payment

- Boston: $26,669 affordable purchase price/$520 maximum monthly payment

- Houston: $20,271 affordable purchase price/$396 maximum monthly payment

- Atlanta: $20,000 affordable purchase price/$393 maximum monthly payment

As you can see, the Interest.com numbers are well below the average purchase price of a new vehicle. This suggests that car shoppers are grossly overestimating or simply aren't informed about how much money they can really spend on their transportation.

Experts say that, as a general rule, you shouldn't spend more than 20 percent of your take-home pay on your car. To find out how much car you can actually afford, calculate that number and use a car affordability calculator, such as this one from Interest.com. This will give you a good idea of how much a car is going to cost each month based on interest rates, trade-ins, taxes and more. You can then compare the cost to your monthly budget.