I did a book trailer for a self-published children's book recently. I did the trailer myself, and it cost nothing. The artwork is mine, and the music was free so long as credit was given. I was very careful of copyright infringement.
Does it look professional? I doubt it. I'm a nearly 50 year old with questionable computer skills. Am I pleased with it? Terribly. It is going to be useful in bumping sales? Probably not.
I did it to post on facebook and my blog. With an illustrated children’s book, I thought the combination of words and illustrations would be more effective than a simple blurb. I made it specifically for things like facebook, so that people already acquainted with me could see if they might be interested in the book. In that specific way, I do think it was effective. I got some sales from folks I haven’t seen in decades. I got some sales from people I barely remember from high school, and a few from strangers. Having done nothing else yet to publicize the book, I can only believe these sales came from my short facebook campaign, which was predominately the trailer.
If you want to see it, you can click on the bunny in my sig, but no hard feelings if you ignore it completely. As I said, I made it mostly for facebook.