The 2-bottle pack is listed at $158 plus shipping. The page gives no figure for the shipping.
The two larger packs ship free, so the 2-bottle pack is the only one where the final cost depends on a number you cannot see. Shipping can also vary by address.
So the real cost of the smallest pack is $158 plus an unknown, and cost per day cannot be completed until you know it.
The shipping amount should appear on the checkout page before you pay. If it does not, stop and ask. Add it to $158, divide by 60 days and compare the result with the larger packs on a like-for-like basis. Our existing guide on the 2-bottle package covers the same point from the pricing side.