It depends on the year, if it's a 1964 Kennedy half, it'll be worth $9 in MS60 condition, but if it's a lower grade the minimum value will be $5, since that's the melt value since 1964 is the only year in which the coin was made in 90% silver. From 1965 to 1970, the Kennedy halves were 40% silver and in MS60 condition will be worth $4. From 1971 on forward, they don't have any silver in them and unless they're in at least MS 60 condition they'll barely be worth more than face value, which even than, a Kennedy half dated 1971-1974 will only be worth $3.50 in MS60 condition. The Kennedy halves with the bicentennial reverse will be worth $4 in MS60. The Kennedy halves dated 1977, 1979-1981, 1983, 1984, 1989, 1990, 1994-1997 and 1999-2001 in MS60 condition will be worth $3.
The post-Bicentennial Kennedy halves that are worth $3.50 in MS60 condition are the 1978 Kennedy halves (from both the philadelphia and denver mints), the 1979-D, 1982 (both mints), 1985 and 1986 (both mints both dates), 1988 (both mints),1991-1993 (both mints), and 1998 (both mints).
The 2002-2004 Kennedy halves are worth $4 in MS60 condition and the 2008 Kennedy halves are worth $1.50. I have left some of them out, but if you have any Kennedy halves, I really doubt they're uncirculated and even than, the prices I just quoted are the prices you'd pay if you were to buy them from a coin shop, if you were selling them to a coin dealer, you could probably expect 60% to 70% of those prices at best (assuming you have uncirculated coins and not circulated, which if you do have kennedy halves you're looking to sell, and you got them out of circulation, they're probably circulated, so in that case, expect 60 to 75 cents apiece, if the coin dealer will even buy them from you)
The post-Bicentennial Kennedy halves that are worth $3.50 in MS60 condition are the 1978 Kennedy halves (from both the philadelphia and denver mints), the 1979-D, 1982 (both mints), 1985 and 1986 (both mints both dates), 1988 (both mints),1991-1993 (both mints), and 1998 (both mints).
The 2002-2004 Kennedy halves are worth $4 in MS60 condition and the 2008 Kennedy halves are worth $1.50. I have left some of them out, but if you have any Kennedy halves, I really doubt they're uncirculated and even than, the prices I just quoted are the prices you'd pay if you were to buy them from a coin shop, if you were selling them to a coin dealer, you could probably expect 60% to 70% of those prices at best (assuming you have uncirculated coins and not circulated, which if you do have kennedy halves you're looking to sell, and you got them out of circulation, they're probably circulated, so in that case, expect 60 to 75 cents apiece, if the coin dealer will even buy them from you)