For example, there are many popular textbooks about medicine. In psychiatric region, Kaplan & Sadock’s is most essential one. Almost all beginner psychiatrists are struggling for reading and understanding this. It costs about $90 in Amazon.com.
In general, books for limited readers tend to be expensive. The reason for this publishing cost. Bestsellers are printed well. If publisher print a large amount of books, the cost for each book will be decreased. Paperback hit the market with cheap price. Besides, books dealing a maniac theme are not selling well. So publisher cannot print a lot. The price increases. Academia textbooks are one of the examples.
Moreover, few people can write books about maniac themes. Few people can edit them. Personal expenses tend to be increased as well.
However, the environment around publishing has changed. Desktop publishing with PC or Kindle Store are now available. Digital publishing made cost for print free. Risk for dead stock is avoidable. That mean we can create a book of maniac themes with extremely low cost.
Now, personal expenses can be cut down. Writers of textbooks are professors of the university in general. They do not write textbooks to earn money to live. They teach their pupils to get money. Writing textbooks are one of tools to teach pupils, or raise their reputation. Many professors want to publish their own textbooks, even for free.
I also have written some textbooks as a co-author. I received no money for this task.
If textbooks are delivered to many pupils for free, they can learn about their specialty, not be annoyed by financial problem. Better education can improve whole society.
I want to write another textbook of psychiatry for free, to deliver whoever want to learn about psychiatry.