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Jay Leno learns the value of the one-of-a-kind 1966 George Barris Supervan

Being unique, and being featured in a film, can both often increase a car's value. But, as childhood friends Jay Leno and Donald Osborne, an automation valuation expert, discover while appraising three cars on Wednesday's episode of CNBC's "Jay Leno's Garage," that's not always true.

In fact, appearing in a bad movie can cost you. A lot.

Here are the three vintage, mid-century cars Leno and Osborne consider as they try to guess which has appreciated best.

1. 1955 Messerschmitt KR20

This car was designed to smile and to make viewers smile too. Its headlights are the eyes and its wide-set wheels the grin. After WWII, Germany was prohibited from producing any vehicles to be used for armament or weaponry, so the country built small, commuter cars like the Messerschmitt.

Powered by a 250cc motorcycle engine, it only fits two people. "Two very tiny people," notes Leno.

"And how hot would this be really in the summer time?" he asks. "This is like driving a magnifying glass. You could burn ants with this thing in California."

It originally sold for $1,070.

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2. 1962 Fiat 500

Many of the Fiat's original buyers were moving away from bicycles and purchasing their first car. "This is the car that really put postwar Italy on wheels," says Osborne.

The original price tag $1,098 for the off-white car bought you a 13 HP 499cc engine and a pair of so-called suicide doors.

3. 1966 George Barris Supervan

This is the only car of its kind. Originally called the Love Machine, it became known as the Supervan and was featured in the 1977 movie that shares its name. Finally it appeared as the public transport bus in the 80's classic "Back to the Future."

"When a creative person passes away," says Osbourne, referring to The King of The Kustomizers George Barris, "the items that they've made skyrocket in value."

That's something to consider when you guess the value of this car. Five years ago it was worth $100,000.

So which car appreciated the most? You might be surprised. Watch the video to find out.

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CNBC's "Jay Leno's Garage" airs Wednesdays at 10 p.m. EDT.