Cecilia B. DeMille says “I’ve had several friends with debut novels this year who have arranged for near-Hollywood-style book trailers. I have no idea how much this costs. I’ve seen others that were self-made using software that came on their computers. Some of these are terrific; some not so much. I hope to soon find a publisher home for my middle grade novel. How big a deal is this book trailer thing? Am I expected to have one? Will I need a second mortgage to make a decent one? Do I have to hire a film company, actors, acquire costumes, etc.? I find the whole idea scary, and truth be told, a little gratuitous. I’m a writer, not a movie producer.”

Ah, the movie trailer. It’s become more popular, but it is not essential. You can have one made through a media designer (such as digital weavers ) for about $500-$1000 which usually includes promotion to get top google hits and utube. Or you can make one yourself (or get a tech savy friend) on QuickTime or IMovie.
Many of my editor friends admit they don’t know if a trailer reflects on sales at all, it all depends on how the author promotes it. Some publishers will use an author’s trailer (whether professionally done or “home-made”) on their websites along with the book. Marketing folks don’t mind extra marketing from the author.
My author friends who do trailers like to have some “thing” to show off their book and a trailer has kind of replaced the postcard mailer that authors used to do.
Trailers do make books look like movies, but this is a way to compete with all else in the media. An uphill battle–poor little books need all they can get.
I repeat-you DO NOT NEED A TRAILER for your book. In fact, if you’re not up for promoting it all over the place, it is not going to do anything for you. If you ARE UP FOR PROMOTING it and using it as an advertising tool then do it. It can’t hurt!
All that being said, and in spite of my own skepticism about trailers, I just did one for my upcoming picture book. Actually I had a friend do it. It’s very simple–some music, images from the book and a few teaser lines, then the cover and publisher. It makes more sense (I think) for picture books since images from the book are already there. Mom Blogs might use the trailer if they review the book. I’ll post it on Facebook for fun, and my publisher said they’ll post it as well. Ask me in six months if it did anything at all. But it IS fun to look at, and reminds me that I have a book coming out!

First and MOST essential, get a publisher for your book and then think about the marketing side. The marketing department can also advise you on all this. Mine is just one opinion. Best of luck to you!!!