I cannot tell you how much I love the idea of making a book trailer. Aside from being an author, my greatest dream is being an actor. Furthermore, I know lots of actors, so conscripting some talent wouldn't be hard. Ditto for a lot of the other talent - costumes, props, film editing, etc - that goes into making a film clip of any length. The budget may be tight, but I bet I can get it done.
Even if I can't get a full-on filming done, a voice-only book trailer is also a possibility. While the next story of the Wandering Tale ripens for awhile, that's what I've been doing; writing the script for both a film and pure audio version of the teaser. It's both great fun and very challenging. I discovered when writing the original synopsis and queries and summaries for my book that it's damned hard to just condense 160k words into less than five hundred. The summary you can find in this post is one of the better ones I managed to write, and I'm still not particularly happy with it. It's yet another skill that the indie author needs to hone, but all-too-often isn't warned about until the time comes to use it.
Either way, writing a teaser script is fun. It isn't my first foray into script-writing, at least, and being a performer myself I have some sense of what can and will sound good when actually given voice. That's another fun aspect - I've been playing around with Audacity and my mic, recording the most dramatic lines over and over and adjusting the pitch and what not. It's amazing how much cooler these things sound when you bring the audio down a couple octaves. Deep voices are one way to hack the human perception of coolness, I'm sure.