Thanks! I've added a section at the bottom of the site showing some real photos of an actual coloring book I got in the mail. There are thumbnails of all photos uploaded on the back.

$24 + postage is the lowest I could reasonably charge for this. Printing costs are a bit more than half of that, OpenAI charge a surprising amount for image generation, but there is also a good amount of human effort (and creative choices) in generating the book. It's not a fully automated process and I hope that's evident from the quality of the end product.

It’s not cheap, but my kids treasure coloring books for a long time and probably one like this until it falls apart.

To the author, I have this idea, for each page, put a sheet of transparent plastic or something like that. So the owner will color the plastic which can be erased. But it may increase the cost anc the color may not stick to the plastic.