[Hijack on the book industry in general]
I worked in a local bookstore for 4 years. Learned a lot there. Just to throw some more wood on the fire...
For large local bookstores, the kind that can afford to buy in quantity with the publishers, they can get as much as a 42% discount off cover price. So, a $25 is a $14.50 cost to the bookstore.
Based on Djeta's estimate of $4 to produce the book, that is $10.50 in gross profit. Keep in mind that the publisher has to pay employees, insurance, electricity, etc. Those types of things eat up gross profit pretty fast.
The local bookstore has $10.50 in gross profit for this same book. They have to pay for shipping, employees, insurance, electricity, etc. Once again, gross profit disappears in expenses pretty fast.
Now, for contrast, smaller local bookstores often cannot buy from the publisher. They go through a distributor (Often Ingram). In these cases, they only get a 35% discount (or less). The distributor takes a cut in the middle. That extra 7% can make a big difference!
The chain bookstores cut better deals (Barnes & Noble, etc). They often negotiate deeper discounts and buy in quantity to get free shipping. Often, they have it drop shipped directly to their stores. These little perks are part of what enable them to offer a 10% discount on hardcover best sellers, etc.
It gets to be a rough market.
Now, when I worked in the bookstore, RPG books usually had a 50% discount! They were a little better in the profit margin, but they stil weren't all that appealing (from the business side) since they didn't sell very fast. Basically, they would tie up inventory dollars and might not sell more than a few copies a year. So, despite my efforts, it was always hard to get them in stock.
I would be interested in hearing how the pricing structure compares to the game stores. But, that is discussing business and people may not be comfortable with that. I understand!
[End Hijack]
My current group of DnD/d20 books is holding out pretty well. 2nd Ed books were less resiliant. Except for Unearthed Arcana, my 1st Ed books are still going strong. Despite years of abuse. The second worst one is my DMG, which had the binding stomped on at one point. Still opens just fine, but the binding feels a little weird.
Of course, I do live in a high-altitude desert. Humidity is not much of an issue.
One of my players has a 3.0 PHB that has fallen apart, but to hear the other players talk about it, it is much more due to abuse than any defect in the binding.