![rare penny](https://a57.foxnews.com/static.foxnews.com/foxnews.com/content/uploads/2018/09/1200/675/rare-penny.jpg?ve=1&tl=1)
This undated image provided by Heritage Auctions shows a 1793 cent made by the U.S. mint in Philadelphia. The penny went up for auction at the annual Florida Numismatic Convention in Tampa, Fla., this week. (Heritage Auctions via AP)
TAMPA, Fla. (AP) — When is a penny worth $300,000?
When it's one of the first copper coins struck at the U.S. Mint in Philadelphia, in 1793.
The annual Florida United Numismatists (FUN) convention was held in Tampa this week. It's considered one of the five largest coin and currency collectors' shows in the nation, experts say, and three historic coins, including the pricey penny, went up for auction Thursday evening. In all, the auction drew $24.9 million in sales.
Mark Borckardt, a senior numismatist with Heritage Auctions in Dallas, said the George Washington-era penny is one of about 500 in existence.
![rare half dollar](https://a57.foxnews.com/static.foxnews.com/foxnews.com/content/uploads/2018/09/1200/675/rare-half-dollar.jpg?ve=1&tl=1)
This undated provided available by Heritage Auctions shows a 1838 half-dollar minted in New Orleans in 1838 that went up for auction at the annual Florida Numismatic Convention in Tampa, Fla., this week. The coin is one of the rarest and most enigmatic coins in U.S. history. Only 10 examples are known to exist in the world. (Heritage Auctions via AP) (This undated provided available by Heritage Auctions shows a 1838 half-dollar minted in New Orleans in 1838 that went up for auction at the annual Florida Numismatic Convention in Tampa, Fla., this week. The coin is one of the rarest and most enigmatic coins in U.S. history. Only 10 examples are known to exist in the world. (Heritage Auctions via AP))
Other high-value U.S. coins sold at auction included a half-dollar minted in New Orleans in 1838. It was one of the first 20 produced there.
A $4 gold piece called a "Flowing Hair Stella," sold for $750,000.
![rare coin](https://a57.foxnews.com/static.foxnews.com/foxnews.com/content/uploads/2018/09/1200/675/rare-coin.jpg?ve=1&tl=1)
This undated image provided by Heritage Auctions shows an 1880 $4 gold piece called a "Flowing Hair Stella," considered one of the great rarities in America gold coins. The coin sold at auction for $750,000 during the annual Florida United Numismatists Convention, in Tampa, Fla., on Thursday, Jan., 4, 2018. (Heritage Auctions via AP) (This undated image provided by Heritage Auctions shows an 1880 $4 gold piece called a "Flowing Hair Stella," considered one of the great rarities in America gold coins. The coin sold at auction for $750,000 during the annual Florida United Numismatists Convention, in Tampa, Fla., on Thursday, Jan., 4, 2018. (Heritage Auctions via AP))
"It was an experimental piece that the government produced, hoping to create an international coinage," Borckardt said. "It's literally the forerunner of today's Euro. The government finally decided no, that's not going to work."
There are only about 15 to 20 of those quarter-sized gold coins in existence.
The coins had high value due to their rarity and excellent condition.
"Collectors interested in these have a very strong sense of history, both American history and financial history," said Borckardt.