Google rolls out digital textbooks, to buy and rent — but students should shop around

Google (s GOOG) has launched a digital textbooks section of Books on Google Play in the U.S., as promised. The textbooks are available through the Play website, Android and iOS (s AAPL) apps.
Most of the textbooks are only available for purchase, but a few are available to rent, too. Amazon (s AMZN) and Barnes & Noble (s BKS) also rent digital textbooks, and when I compared prices across the stores, I found variability in both availability and how long the rental periods are.
Take the Psychology textbook by Daniel Schacter, for instance: At Google, it’s only available as a rental, for $65.99 for 180 days. The textbook isn’t available in a digital edition at Amazon at all, but students can rent a print copy for $25.23 per semester (a period ending January 4, 2013), with the option to extend the rental for $5 every 15 days. And at Barnes & Noble, the digital textbook rental¬†is $1 cheaper than Google’s: $64.99 for 180 days.
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Google also has fewer digital textbooks for rent than Kindle or Nook, but the selection should increase over time. Google says it’s working with the five largest textbook publishers —¬†Cengage, Wiley, Pearson, McGraw-Hill and Macmillan.