Have you self-published a book at Amazon's CreateSpace.com?

It's basically a do-it-yourself service where CreateSpace can pay for the cost of the ISBN. However, the book is sold only at Amazon if you didn't pay for the ISBN registration. Of course, I thought that's a good deal since you want to sell at Amazon.com anyway. If I remember right, you will be submitting an electronic copy of your book. It's most probably a PDF. There is no cost to you, but CreateSpace will get a big chunk of the earnings. I think the biggest cost in this "free" service is the cost of ISBN registration. And that largely determines your earnings.