Nothing is completely free. If you are willing to devote your time instead of money, there are numerous ways:
- through your blog
- through social media
- through forums
- through mailing lists
The trick is to find people who would be interested in your gig (try to understand their needs as much as possible), find the places, where they are hanging, and promote yourself in visible, although not spammy way. For instance you should become respectable member of certain forum and only then include a link to your page, promoting your services in your forum signature. This works like a bomb, but it takes some time. As I said, nothing is completely free.