Here is a motivational video on metal detecting were over twelve years Don has found $13,000 in gold and jewelry. My favorite is the 50 BC Celtic gold stater coin.
The 1/6 Stater coin is about 2,700 years old. This old coin was only stamped on the one side. Originating out of Lydia, known as part of Western Turkey, this could be the oldest coin found to date. It's in the main exhibit in the Department of Coins and Medals of the British Museum. This coin was made with electrum, an alloy of gold and silver. It is believed to be from the dynasty of the Lydian king, the roaring lion Alyattes (about 610 - 560 BC) or perhaps his predecessor Sadyattes could be behind the royal blood line. As much as I looked for the price of something like this, nothing has turned up, I'm guessing it could be priceless.
The 1955 Double die was mistakenly printed in Philadelphia. At first they printed 40,000 of these before they caught the problem. 24,000 were released and the rest were destroyed. Depending on the condition one can be worth anywhere from $500 to $15,000.