Whilst in the grocery store I saw a bit of cheese. The sign said ¥210. In this scenario, it is important not to jump to the triumphant glee of serendipitous circumstance phase. For future self, these are the steps:

Step One:  Note that the stated price is per unit of measure and NOT for the whole chunk of whatever it is.

Step Two:  Check the label for the actual price for the item by weight.

Step Three:  Gasp in horror.

Step Four:  Put that thing back and walk away.

By following these simple steps, it is possible to avoid becoming the sheepish owner of an inordinately expensive bit of a clearly unnecessary luxury item.