I don’t know about the prices of textbooks but for new hardbacks the Kindle price is at least forty percent cheaper because of the savings on paper and distribution. New releases used to be a standard 9.99 in price but that’s inched up. Check any new release on Amazon - they always list the Kindle price if available on Kindle. Paperbacks on Kindle are usually equivalent to the Walmart discount and no charge for taxes. A 5.99 paperback sells for 4.12 at Walmart and that’s often the Kindle price too.
E-readers are fueling the growth of online publishing and providing writing opportunities for writers of racier content. A lot of adult entertainment is downloaded in the privacy of one’s own reading device. Not just smut, but content to satisfy the reader’s desires for another Harry Potter or Twilight. What the big publishers don’t deliver in time to satisfy a trend, some writer will post online for download and it will sell.