>The answer is, you can't.
But you can make them cheap. If companies can make flimsy electronic devices or appliances that fall apart after a few years, why can't publishers do the same with books? Why do textbooks have to be printed on photo paper, with hard covers and Smyth sewn binding that lasts a couple of decades? Why not print them on lower quality paper and use thermal binding of the kind you find on paperback novels? And for crying out loud, not every book needs to be printed in full colour. I understand you need colour photos for, say, a pathology textbook. But a cash-flow diagram in a basic economics textbook looks just fine in black ink. As do titles and subtitles.
Mind you, this isn't some wild fantasy. In fact, the very same publishers that people are lambasting in this thread publish "low-price editions" in other countries that are exactly like the ones described above. In India, for example, this two hundred dollar textbook can be purchased for about ten bucks. It lasts a year or two before the pages start falling out, students buy new books/editions by choice, and the publishers stay in business.