Amazon is going to offer a service soon that allows you to purchase a eBook/Kindle version of a physical book you've purchased from Amazon for a low cost ($0.99 - $2.99).

This would allow you to get both physical and electronic versions for about the same price.

http://www.theverge.com/2013/9/3/4689346/amazon-kindle-matchbook-bundles-physical-books-with-ebooks

I'm not sure when this program starts.

HTH,

Rob