well if its biz entertainment, can claim one den its fine..
its not about the true value of the food, is they din highlight to u.
u do have a case not to pay n u have high chance of winning one..cos tis kinda mushroom is rare n very high value..the judge will expect the resturant to highlight the price esp if u din order...if the cef just come over n give, no one will ever know..u can actually sue the resturant in trying to cheat biz