You're saying that the middle cost is significant. That suggests that the latter cost is also significant. Therefore lowering the dollar price of the book has little effect on the total in the above equation.
Let's put it another way. When do avid readers start reading a new book? When they finish or get bored of their previous book.
Even if we agree that the total cost (including time) of acquiring and reading a book is high, that does not indicate that demand is inelastic.