CoinTrackers.com has estimated the 1964 Kennedy Half Dollar value at an average of $10, one in certified mint state (MS+) could be worth $90. (see details)...
1964 Kennedy Half Dollar
Type: Kennedy Half Dollar
Year: 1964
Mint Mark: No mint mark
Face Value: 0.50 USD
Total Produced: 273,304,000 [?]
Silver Content: 90%
Silver Weight: .3617 oz.
Silver Melt: $5.35
Value: As a rough estimate of this coins value you can assume this coin in average condition will be valued at somewhere around $10, while one in certified mint state (MS+) condition could bring as much as $90 at auction. This price does not reference any standard coin grading scale. So when we say average, we mean in a similar condition to other coins issued in 1964, and mint state meaning it is certified MS+ by one of the top coin grading companies.