--put the item back. You don't have to buy it at that store...promise.
--purchase the item, and decide that you must have had an unrealistic price in mind. It happens. I thought Advil was going to be like three bucks.
--text a friend something like this: "Ohemgee...[said item] is so much more than I realized!!" That way if the friend agrees, s/he can say so, and if not, no big...because you haven't physically confronted anyone.
Things NOT to do when you're about to purchase something, but you suddenly realize that it costs more than the "reasonable" price you somehow arrived at in your mind:
--say anything like this loudly: "WOW!! FIFTY BUCKS FOR A VIDEO GAME?" or "THREE FIFTY FOR A CUP OF COFFEE? ARE YOU SERIOUS?" I promise you--the answer will be yes.
--turn to the stranger behind you in line and complain about how you just can't believe the cost of items these days. Odds are, that person looked at the price too, and is still in line, ergo they CAN believe it.
--repeatedly look at the price sticker and outwardly sigh, snort, scoff, etc. It's a sticker, and no one with decision making power is observing how you interact with the sticker.
It's not worth it. No matter how many of those things you do, the price of the item won't change, and the person who works behind the counter who very likely did not set the price of the item won't start to like you more.
PS: none of this applies at the Swap Meet. Go crazy out there.