For several reasons, circulated 1964 Kennedy half-dollars are cheaper than either the Walking Libertys or the Franklins, the other two half-dollars commonly available. Although minted only one year, 277.3 million 1964 Kennedy half-dollars were produced. By comparison, only about 477 million Walking Liberty half-dollars were minted during their 32-year life. And, during their 16 years of use, only 309.4 million Franklin half-dollars were minted.
Kennedy half-dollars disappeared from circulation almost immediately after being minted. The coins carried the image of a popular president who had been assassinated only a few years earlier, and they were the last 90% half-dollars minted. In 1965, the Mint removed all silver from dimes and quarters, and reduced the silver content of half-dollars to 40%, which are now known as 40% clad halves or 40% Kennedys. Clads carry dates of 1965-1969. This change heightened the hoarding of all 90% silver coins but especially the Kennedys.
Further, in 1964, the Treasury had ceased redeeming silver certificates for silver dollars and started giving silver bullion instead. In 1968, the Treasury ceased redeeming silver certificates at all. This added to the popularity of all U.S. 90% silver coins. Consequently, few 1964 Kennedys circulated, which meant that few, if any, became worn enough be destroyed by the Mint as had millions of Walking Liberty and Franklin half-dollars. So, today, Kennedys are more abundant than Walking Libs and Franklins, which results in the Kennedys being cheaper.
A half-dollar contained 0.36169 ounce silver when minted; a $1,000 face bag contained 723 ounces. A bag of halves ($1,000 face) weighs right at 55 pounds on a bathroom scale and will net 718-720 ounces of silver if smelted. A bag of dimes or quarters will yield about 715 ounces.