I agree. When I buy through Amazon Prime, I can safely buy with one click because I can see the exact price I will be charged and, usually, the exact day it will arrive. For next day delivery, I can't recall they have ever missed the date.

It's logical that they add the cost of shipping to the item price, but their cost must be much lower than alternative sellers, as it is hardly noticeable on low-cost items, and comparable to prices charged by Walmart, etc. who charge extra for shipping.