How much is 100 percent solid gold miniature of the US of America's saint-guaden's 20 gold piece worth?

Such a coin isn't a real coin and has absolutely no collector value. Rather any value comes from the precious metal content (if any) in the coin. I would take it to a jewelry store or a refiner and have them test it and see how much gold is in it (if any) and then sell it for the price of gold because such a "coin" has no collector value at all.