According to this http://www.coinflation.com/coins/1965-1970-Silver-Kennedy-Half-Dollar-Value.html , the half dollars are worth .854635461 BTC at its current market price.
Actually that's the value of the raw metal in the money, but if see the auctions below you can found that 3 coins worths about 1.73703703704 BTC (0,579BTC/cad) few minutes before the end of the auction, while some other another auction arrives at 0,82-0,86BTC but I think that is more for collectors effect than for investments.
Here in Italy is possible to find silver eagle dollars sold in coin shop at prices 40-50% over the spot, and some old silver coins like 500lire is sold at non less of 2BTC for collectors with top of 4-6BTC, while actually that coin worths less than 1,6BTC in metal (11grams of silver 825/1000). But other coins with the same amount of silver but larger mintage are sold at 1,3-1,4BTC.
