Printing cost of a paper book is only $3-4, so even eliminating the cost of printing, ebooks would still be expensive. I suspect most of the cost of books goes to marketing and promotion, not printing and binding.
That's the difficulty with books. People fee like they've paid for the physical object in their hands, when really, they've paid for all of the work that went into making that object possible.
http://www.millcitypress.net/book-printing-costs.aspx