It's a lot harder to quantify, and it would be irrational to do so here. I mean, how much are you really going to grieve a $3 shipping cost? It comes down to

It's a lot harder to quantify, and it would be irrational to do so here. I mean, how much are you really going to grieve a $3 shipping cost? It comes down to paying for the convenience of not having to "worry" about the shipping costs. Personal example: To get to (and from) my boat during boating season I use a launch service. I can pay for the season up front, or I can pay by the ride. The season ticket gives me, let's say, 30 round-trip rides to and from my boat. 30 boat rides is a lot more that the average person actually uses the boat in a normal season. So at the beginning of the season I can do the math (vacation, work schedule, and so on) about likely usage, then make a decision. If I think I'm going to get out 20 times, I can just say "to heck with it" and get the pass. I'm paying for the convenience of, say, not having to go to the bank every few weeks and get a bunch of bills for the ride. This is a fee I pay for that convenience, and I may end up breaking even after all, and what-not. But when you buy that item on Amazon you don't have that situation. You're not changing your payment structure- there's no inconvenience if you pay the shipping then or up front (if you had to re-enter your cc for a separate shipping payment you could argue it was one of convenience). You're simply going through the exact same steps as before and spending less money. Now, if you are arguing that the analysis is up front with your Amazon Prime membership payment at the beginning of the year (like my boating analysis)- estimating your likely shipping charges, then going with Prime if it looks close, then I would agree with you. But I agree with the original argument-that the convenience of paying more for not having to worry about shipping costs is an irrational behavior, as an economist would define it, one based on emotion rather than an economic analysis.