This is an exceptional example of the limited production Accented Hair Proof Kennedy Half Dollar graded MS66 by NGC certification #1997562-008. NGC Population for grade 4778. Due to history of President Kennedy coins in circulation were hoarded by the public and have always been in demand by collectors. This beautiful 1964 proof  will make a wonderful piece for any collection. 
There are no firm numbers on exactly how many 1964 Accented Hair Proof Kennedy Half Dollars were struck, but estimates suggest only between 50,000 to 100,000 rolled off the presses. That means the Accented Hair design accounts for less than 5% of the entire Proof mintage run of 3,950,762 examples. Values for this scarce type range from about $50 to $75 for a typical example in the range of PR63 to PR65. However, superb examples graded PR68 or higher can fetch $350 or more. One of the highest prices ever achieved by this coveted Kennedy Half Dollar rarity was realized at a September 2017 ( excerpt from Telling a 1964 Accented Hair Proof Kennedy Half Dollar Apart From Regular Kennedy Halves  by Joshua McMorrow-Hernandez)