A good or bad book cover can make or break a good book
http://www.thecreativepenn.com/2010/06/17/choosing-the-best-book-cover-designer-for-your-book/
How much do I Charge for my Ebook? http://www.digitalbookworld.com/2013/what-is-the-value-of-an-ebook-hint-it-has-nothing-to-do-with-the-cost-of-paper-and-ink/