"The Printing process costs, on average, 10% ($4) of the cover price of a book, "
So, "Printing Process" is not a function of the cover price of the book. It is a function of what size of book, spine design, what type of binding, what type of covers, whether there is printing on the inside of the cover, whether there is color, what type of paper, and how many pages, and how many books you will be printing.
For example, sitting on my bed right now are two softcover books:
"Maps in a mirror, short fiction of Orson Scott Card", 671 pages, $23.95 list.
"Advanced Unix Programming, Second Edition", 717 pages, $64.99 list.
Both Black and White, perfect Binding, color cover, no printing on inside of covers.
http://www.instantpublisher.com/Price-quote.aspx sugests that the cost of each should be $4.72 - which is 19% of the Orson Scott Card, and 7.2% of Advanced Unix Printing.
In addition, this is what it would cost _me_ - I have to believe that large publishers are able to print their books for less that what I would pay.