For the past few years, when I can't find an interesting Nook book for less than 5 bucks, (hey ... I'm Scot/Irish ... wanna make something out of it!?) I've been buying books from an online used book store by the name of: betterworldbooks.com.
Go to the site's press page, which is in the About Us section of the site, for more information about the site. As you'll see, it's a business that gives a significant percentage of sales to various non-profit groups to help support literacy programs around the world.
They are very "green-minded" and very aware of the carbon footprint upon the environment, e.g., if you have some used books that you'd like to keep out of the local landfill then you can donate them to BWB and they will send you the postage to help you make that happen.
They accept PayPal (and other forms of payment) with FREE shipping ... usually shipping in 1-2 business days with delivery generally in 5 business days within the continental U.S.
Over the years I've used many online used book re-sellers and Better World Books is clearly the best one I've had the pleasure of dealing with.
I have no financial interest in their company but I do highly recommend them!
S.
