Markets in Everything: Kindle Textbook Rental
"Amazon's Kindle Textbook Rental is a flexible and affordable way to read textbooks. You can rent for the minimum length, typically 30 days, and save up to 80% off the print list price. If you find you need your textbook longer, you can extend your rental by as little as 1 day as many times as you want and just pay for the added days."
One example is "Fundamentals of Financial Management" by Brigham and Houston, which has a retail list price of $186.95, sells in hardcover on Amazon for $142.27, or $107.16 for a Kindle edition, and $40.03 for a 60-day rental, $47.09 for 90 days, and $51.01 for 120 days.