Fifty cents unless it is in mint condition. Even then the 1976 bicentennial half dollar is not very old or rare. If you want to know what a mint condition coin is worth, I suggest a coin pricing guide.
Bicentennial half dollars were never minted in silver
I'm trying to find the sale value of some 1776-1976 Eisenhower Dollars and some 1969-1992 Kennedy half dollars
If it's not minted in silver it isn't worth anything. If it is though, then it is worth like $5.