to CoinTalk dingbat (your description, not mine ) At the current bullion price of silver it's worth at least $3 +/- 10% depending on whether you're buying or selling. Depending on its grade and variety, it might be worth more than $20, but excellent quality pictures of both sides would be necessary to even make an educated guess.
Look on ebay. That'll give you the best idea of it's worth. You have to realize that they minted a couple of hundred million of them so they are mostly sold for melt value only. Even the really good condition ones aren't all that expensive.
The silver value as of today is $2.96 for the 1964 half dollar. You could buy for about $3.25 and sell for around $2.60.
Interestingly, my wife picked up 12 halves at the credit union today [it's all they had] because she knows I like to look at them. There was one 1964. The people at the credit union thanked her for taking them because they don't want them. Very lucky.
It seems as though the people are hurting financially these days I buy 4 rolls of halves a week from the bank and have gotten about 20 1964's and about 40 clads in the past month not to mention the silver coins I have found in circulation the last few weeks. My buddy at the gas station told me he found a 1909 penny and asked me if I wanted it and it was a vdb but not and S. If these people only knew what they were spending they would kick thereselves. That good for people like us though.