What is a 1789 US mint coin worth?

What you have is a mint token struck on a penny-sized blank. These are included in the uncirculated coin sets issued each year, one for Denver and one for Philadelphia. 1789 is the year that the Treasury Department was established, not the date the token was made.

Sometimes people break up the sets and the tokens slip into circulation because they look like pennies. However, they aren't collectible because they don't have a mintage year on them and they all look alike.