When I was in the motorcycle parts business, a trade magazine published a report on overhead etc. vs. sale price.
You must mark up your total cost (wholesale price + shipping) by 28% just to break even. Any discount larger than 22% from full retail price means you lose money on the sale.
My current products have a production cost of $ 4.86 (or less) including delivery to me, and sell for $19.95 (or less), so I can be generous and offer volume discounts.
Obviously, the net cost does not include many thousands of hours spent researching & writing these articles. http://www.victorylibrary.com/books1.htm