There are some things you can do that cost you nothing that can help you build a following for you book in your spare time without even leaving your house.
What magazines do you read or are you aware of on the subject of your book? Find the websites of these magazines, and look for their submissions guidelines. Sometimes there is a link for them, and sometimes you have to go to the “Contact Us” section. You could submit articles to them either that you write new or that are excerpts from your book. This is a great way to publicize the book. When you write articles, you often get to write your own bio, and you can include in the bio that you are the author of your book. You can even direct people to our website to buy it, where you get 40% of the retail price for every one sold. And sometimes magazines pay you for articles like this. In fact, the vast majority of people who earn their living writing are freelance writers. Their book is only a part of their income.
You can also find new magazines, blogs and forums where people have conversations about this subject. To find them, go to Google and type in some key words from your book followed by “magazine”, “blog” or “forum”. Blogs and forums are communities of people who gather around similar interests. One of the factors in Google’s rankings is the number of readers or participants, so a simple Google search like this will yield the best results on the first page. Join the community and post comments on blogs and responses to the forums. When you sign the response, sign it with your name and the title of your book under your name. Sometimes you can even include a link where people can buy your book. (Look for a box that says URL when you are posting your comments.) Since these people are as passionate about your subject as you are, I’m sure you’ll enjoy it and even make some new friends.
Another way to get your name out without leaving the house is to get Google to do some work for you. You can use Google alerts to make sure you’re on top of every news story that is related to your book. Terry Cordingley has written a great post about this: http://terrycordingley.blogspot.com/2010/03/google-alerts-publicists-secret-weapon.html
Do a little every day to get the word out about your book, and you’ll see success.