How much is a gold 100 bill worth?

A gold 100 dollar bill, typically a novelty item or collectible, does not have any real currency value as it is not an official U.S. currency note. Its worth is primarily determined by its collectible value or the price someone is willing to pay for it. If you're referring to a gold-backed certificate or similar, those have historical significance but are not widely used in modern transactions. Always check with a numismatic expert for accurate appraisals.