月と鼈(すっぽん)
■月とすっぽんほど違う be as different as day and night [as light and darkness, as chalk and cheese]
あなたの邸宅と僕の家では月とすっぽんほど違う. Your residence and my house are as different as light and darkness [chalk and cheese, day and night].｜There is a world of difference between your residence and my house.