Oldest and perhaps most intriguing of the three, this high-end fiberglass luxury car is a personal favorite of Osborne. It's powered by steam.
To produce the car, 20th century entrepreneur Robert Paxton McCulloch consulted with Abner Doble, an engineer who designed over 40 unique car prototypes and who is a personal hero of Leno's.
"He produced the greatest steam car ever made: The only steam car where you turn a key and drive away," says Leno. "I have two of them."
The Phoenix never made it to production, notes Osborne, because of hold ups at the steam power plant. Had it gotten to the market, it would have cost around $10,000 in the early 1950s, a time when the average car cost between $2,000 and $3,000.
This one appreciated over 100 percent in the past five years from a value of $175,000 to $375,000. According to Osborne, that's because of a recent rise in public interest interest in one-offs, prototypes and concept cars.
What about the others? Have they appreciated more or less? Watch the video to find out.
Don't miss: Magnus Walker has 25 Porsches that could be worth $7.5 million, but he's not selling
CNBC's "Jay Leno's Garage" airs Thursdays at 10 p.m. EDT.
Video by Richard Washington