Considering most people mortgage their home over 30 years, it is not unfair to use this fact and build onto your math a bit: 2.50 / 30 years = about 8.33 cents

Considering most people mortgage their home over 30 years, it is not unfair to use this fact and build onto your math a bit: 2.50 / 30 years = about 8.33 cents per year in 'storage rent'. Seems pretty cheap to me, when you compare relative costs of storage. Of course, I'm typing this with some sarcasm, because the whole metric is bad. Your analysis assumes that: A - somehow you have unlimited items to store in all the empty places in your house, B - ignores the absolute cost of having empty space (you've already spent on the house, but if you leave that space empty, you have opportunity cost becuase you COULD be storing books), and C - ignores any utilitarian value you get from having the books around. :) Here's a hint: C is most important. And it references back to the point the article is trying to make. It is clever though, so I'll give you that.