Remember the first used car you bought?

I do.

$500 and a case of beer were enough to get my hands on an old Honda Civic a friend in Springfield, Missouri was selling.

Was it a beauty? No.

Was the price right? You bet.

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Most of people bought their first used car by scraping together some cash and buying whatever they could afford.

While that's still the case for millions of people, a new study says millions others cannot afford to buy the average used vehicle in their city.

iSeeCars.com analyzed 25 million used cars sold in the 50 largest metropolitan areas in the U.S. and concluded most would leave the average household over-extended.

"The fact is, buying a used car or truck is just not realistic financially for millions of Americans," said iSeeCars.com CEO Phong Ly. "Even though they do it, the numbers show people are not following the ideal standard to determine if they can afford what they are buying."

Ly crunched the numbers for used vehicle sales following the "20/4/10" standard where used car buyers put down 20 percent, take out a loan no longer than four years and spend no more ten percent of their monthly income on a car payment.