You can currently buy my complete works (Egg Bacon Chips and Beans and Everything I Know About Life I Learned From PowerPoint) from my shop for £20. That is a bargain price, only available because every now and then I buy secondhand copies of EBCB from Alibris, Abebooks or Amazon. They're normally about £4.
But I went to buy some more the other day and you can't get one for less than about £38. Exciting! Either the secondhand algorithms have detected that there's a regular buyer out there (me) or we're getting to the end of the remainder pile and scarcity's starting to kick in.
There's an opportunity there for arbitrage, if you can be bothered. But, if you're the last person on earth who wants those books and hasn't yet got them, now's your chance.