In most cases this was done with a 13 cent stamp. Silver Proof 1974 Half Dollars were minted but these only.
Those issued at the Denver and Philadelphia mint appear to be selling for between $1.50 and $3.00, while the San Francisco specimens tend to sell for $3 to $9 for the proof. The year 1974 saw the United States mint in San Francisco, Philadelphia, and Denver create Kennedy Half Dollars.
