Books on the Knob has details on how you can buy a $10 Amazon GC for only $5.
Books on the Knob is a blog that lists free and discounted e-books. If you have an e-reader (or an app on your computer) you might want to spend some time checking out the latest posts. Be aware, they list ALL types of books. I don't consider the blog kid/teen appropriate, so please do not send the link to your kid without checking it out yourself first. Of course, it's your child, but if you do, don't blame me when your kids asks what 'BDSM' means. ;-)