To buy a new book or to not buy a new book? That is the question.
I know what you're thinking--and, yes, this is a question that hard core book nerds ask themselves. As much as I'd love to have a bottomless book fund, my bank account tells me I have to stop somewhere.
There are a million ways to evaluate whether to buy something. The cost, available funds, level of need, level of want, the amount of joy the item it will bring, etc. I've got a formula to help me decide if I should buy a book or not, and it comes in handy particularly when I'm evaluating new releases, which are almost always more expensive than backlist books.
I look at the length of the book--not just the number of pages, but also the typeface and layout--and consider how long it will take me to read. Based on how fast I normally read, I evaluate how many hours it will take me to read the book. (Checking to see how long the audiobook is can be a good indicator.)
From there, I consider how much I make per hour compared to the number of hours I estimate it will take to read the book, then compare that to the price of the book. Then I take that comparison and stand it up against my entertainment budget (which includes eating out, buying non-survival-necessity items like clothes and books, and gifts for others' birthdays/Christmas/weddings/etc).
For example, I'm at a bookstore and there are two novels I want, but I can only buy one. Assuming all things are equal -- I want both of these novels with equal fervor and they're each $15 -- I would look at the time it would take me to read them to determine the one I should take home.
Alternatively, if I'm at a bookstore and I'm deciding between these same two novels and I find that one is $12 and one is $15, I chose the $12 novel. I do that because, if you're assuming you're going to get the same amount of happiness (utils) from each book, buying the cheaper book will get you more happiness for a lower price.
There are times, however, when this equation doesn't work. If you're buying a trade paperback of a comic (5 issues bound together and sold as a single installment), then it might cost $15, but it'll only take you about an hour to read. Assuming you make $10 an hour and the trade paperback of the comic is $15 and will take you one hour to read it, that doesn't necessarily mean you shouldn't buy the comic. It means you really have to consider the amount of happiness you'll derive from reading the comic and whether you would want to re-read it at some point in the future.
As for a real life example of how I put this equation into action, there's a new book out that I really, REALLY want called Between the World and Me by Ta-Nehisi Coates. Since it's a new release, it's $24 (which is standard for a new hardcover). While I know it's 150% worth every cent, the book has 176 pages, so I know it'll only take me about two hours to read. That's truly the only reason I haven't bought it yet. Since I don't have unlimited income, I have to consider my dollars per hour spent on entertainment, and (at its current price), Between the World and Me is coming out to $12 an hour. There is a high re-read potential, so that's a factor too, which may lead to me getting it anyway. If Books-A-Million wants to email me a coupon or if a bookstore wants to help out a reader with a limited book budget, I'd love that.
I realize my book-buying equation isn't perfect, so I'm waiting in hopes for the day that I have enough disposable income to go on a book shopping spree any time I want. Fingers crossed!