What is the value of a 1986 s us liberty half dollar commemorative coin?

That's a mixture of a very specific question and a super-general one.

If you're asking about a 1936 US half dollar, please see the Related Question.

If you're asking what a US silver coin is worth there's no simple answer. As of 01/2011 common ones with no real value to collectors sell for about 18 to 20 times face value for the metal alone. On the other hand prices can go up to several million dollars for the rarest of the rare coins like an 1804 silver dollar. So it's really necessary to post a question with the coin's date and denomination if you want a specific answer.