Ok, so I'm a little embarrassed to admit this, but it seems that I've been using equivalent annual cost when I shop, and I've never heard of it before!
You see, when I buy something expensive (not something like a house though), I try to figure out what the equivalent cost would be if I used it every day for year, or a certain amount of time per week, or for a certain number of months.
For example, consider a $100 dollar pair of boots. If I wear them all the time during the winter (3 months), really I've only paid $33 a month for the pleasure of wearing the boots! And it becomes even less if I wear them the next year too. All of a sudden, the boots seem like a bargain!
I'm not sure this was the original intent of equivalent annual cost, but it sure makes me feel better sometimes.