Books for college are so pricey because they are written for a limited market and need to follow a syllabus of study material.
Any publisher will be looking at a book and its market value. College books are aimed at perhaps a few thousand students over a 3 year period which means that, given the costs of binding, proof reading, printing and often research, the price of each book will be higher than a mass produced fiction or general interest textbook.
When commissioning writers to produce college books a publisher is using an expert who will need to know the precise content desired, the syllabus and level of study at which the book is aimed and they will often need to carry out detailed research in order to produce an accurate,up to date book on any given topic. Subject material changes and the level of study at college level is deeper than for the general market so the hours involved in writing and researching a textbook are far higher than writing a book for the general market. Not only that but the editors and proof readers used will need to know the subject too so they cost more.
As an example a book on plant anatomy for college would take a great deal more research to get the up to date information given the rapid progress made yearly in detailed understanding of plant cells, functions and microscopic detail than a general, coffee table type of book on plants aimed at a more wider audience. Furthermore, even with all the research and time taken to produce such a college book, the market for a book of this depth will be far more limited than one aimed at the general public.
So, college books are more expensive. The upside of this is that they keep their value. Many textbooks like ‘Strasburger’s Textbook of Botany’ are still as relevant for students 5 years on as they were when bought originally and these textbooks can be sold for a good price second hand to new students. Many college books will become life-long useful additions to your reference books, continually re-used and re-visited if you stay within your study field.
While it would be great if college books could be published and sold with subsidies so they cost less, this could actually be bad for the colleges in the long run as it could encourage publishers to mass produce books for a decent turnover. Many publishers publish college books at little profit because students will remember them as the publisher to go to for their subject field but publishers, like any other industry , have to make a profit to stay in business so each college book will cost more because they still have the same costs to produce them as for any other book.
College books are also often larger than mass-produced books because they need to hold a huge amount of information and be able to be used right through a degree or diploma course so the amount of research, pages and hours spent and needing paying for increases with higher levels of study, making the books costly.
For students, it is worth checking second hand shops and college campus shops for used books and also choosing carefully . Many colleges have a recommended reading list and it is far better to spend a decent amount of money on a few good books which are recommended for your course and tailored for your study area than to buy a lot of cheaper books which may not give the information you need.