What is a 1964 two headed coin worth?

If you mean it has the "heads" design on both sides of the coin, then it's most likely a novelty coin, available for around $6 at a variety of locations. Since it's a 1964 coin, unless it's a nickel or penny, it may be worth slightly more in raw silver value, but it would depend on what coin (dime, quarter, half-dollar, dollar) it is.