Large retailers have AT LEAST two people in charge of making sure items are priced properly. At Wal Mart for example, I cant remember what it is called, maybe the UPC office?? But the person or people who run the UPC office are the ones who set the UPC code into the computer for items and set the price that it scans at, and the other person who is responsible (at least i think they are) is the department manager in charge of that particular department. I used to work at Wal Mart when i was younger, and when they use their "Telzon's" (the UPC scanner device) they (department managers) can change the price of a certain item and also print out a price label with a barcode on it. Those are the little yellow labels you see on shelves. I dont know how Meijer's operates, or even if the way prices are set has changed since ive worked at Wal Mart, but someone either entered the price wrong in the computer initially, or someone made a mistake later on. Either way, it had to have gone un-noticed by at least ONE person, if not more. Someone didn't do their job.
I am with the people who think the OP did the right thing. He at least asked about it. He gave them a chance to check it out. They didn't.
If it were my store, i would be kicking myself, but i would still honor the fact that it was priced wrong and immediately fix it after the customer liquidated the inventory for me. I would have to bite the bullet, because if i were the owner/manager, it would be my responsibility to make sure everything is priced correctly and it would be my fault otherwise. Its not the customers responsibility to make sure the item is priced correctly, however i do think it is the right thing to do morally on the customers part to point it out if they do notice, which the OP did.
If i were to buy a car that i know is worth much more that someone was asking, i would not volunteer to give them what it is worth. I would be out of my mind. It is their responsibility to do the research. And i know private sales are different than retail, but the point is the same: It is the sellers responsibility to make sure the prices are correct before the item is offered for sale to consumers.