If you're in the market for a quick and dirty book trailer, here's a website that let's you create 30-second videos for free. Here's mine.
The best part is, this only took about 10 minutes to make. You just choose a template and music, plug in your text and images, and the website adds all the fancy special effects. Have fun!
This is interesting. Another cheap (if not free) avenue is the one I'm taking: I put an ad online where students at the film school here would see it. I met with a couple of people and am paying one young lady $100 to make a trailer. She's doing it for her resume and as a chance to experiment with genres (so she tells me). She said getting actors is easy because they will work for food and want something on their resume.
(As I type this it sounds a little exploitative, but everyone seems to be getting something out of it, and hopefully I'll get a good trailer!)