You can make the book a PDF and send it via email for free. Or publish it on Kindle and make it free or $0.99. Then you can make the paperback edition cost a few bucks for those who choose to forego the free option.

The principles of book marketing are very simple. Understand that your goal is to write a book that people will recommend via word of mouth. That's the only effective book marketing. Writing a great book people will talk about. The questions you need to answer are: 1) What type of people -- get as specific as possible -- will want to buy your book? 2) Where do these people congregate? (online, in-person, etc.) 3) How can you get the book in front of them? 4) What resources do you already have at your disposal (social media, professional network, family, friends, etc.) -- and how can you get your book in front of them? Before you start, test your idea. Find the audience you want to reach, and write an article, forum post, email -- whatever gets you in front of them. Do you get an emotional response? If yes, continue. If no, tweak or try something else.