Actually, at very high volumes (where the non-recurring engineering cost is sufficiently amortized), the larger equivalent component is more expensive, since you are using more material to manufacture the component.
Obviously, other factors, like process yield can be a factor here as well, since a lower process yield for the smaller component would increase its price.
Obviously, other factors, like process yield can be a factor here as well, since a lower process yield for the smaller component would increase its price.