The 2-bottle pack shows $158 and a note that shipping is extra. No shipping figure appears.
The other two packs ship free, so the smallest pack is the only one whose final cost depends on a number you cannot see. Shipping can vary by address.
Until you know it, you cannot complete the cost-per-day arithmetic for the 2-bottle pack.
The shipping amount should appear at checkout before you pay. If it does not, stop and ask. Add it to $158 and divide by 60 days, then compare with the larger packs: before shipping, the 2-bottle pack is about $2.63 a day, and the 3-bottle pack is about $2.30. Confirm everything at checkout.