A lot of book trailers are boring: The author looking slightly uncomfortable describing his or her book in superlatives, or else telling what inspired them, or trying to give a summary of the plot without giving too much away. I doubt that they prompt many sales and some I've seen probably dissuade anyone from buying the book.
Below is a book trailer that's fun to watch. Will it prompt you to buy the book? Well, I haven't but if I spot it in a bookshop or think of it the next time I'm roaming around Amazon, I might.
Yes, the author has the benefit of professional actors, and what looks like professional camerawork and editing, and I'm not suggesting that everybody could match these. The point is that it's fun as well as revealing something about the nature of the book. I think that kind of relevant fun is possible to do without professional actors.
Having said that, if you happen to live in a city I'm confident there are a lot of professional, semi-professional, and skilled amateur actors there who would be happy to be in a well-written book trailer in exchange for nothing more than a credit, a pizza lunch, and an autographed copy of your book.
There are also quite a few camera operators around who do corporate work and would love to have a chance to do something more creative, especially a project that wouldn't take long to shoot.
For directing and editing you may be able to find talented students at a local college or university. Many are eager to take on a real-world project.
Here's a fun example--it reminds me of a mini-version of a early-to-mid-period Woody Allen film; it's promoting the book, One More Thing by B. J. Novak:
