A provisional patent will give you one year to file a real one, protect your invention the same as a patent would, let you use the phrase "patent pending," and let you start showing it in public, marketing it, etc.
I have followed the "Do It Yourself" patent books before and filed my own, and I've also had lawyers file some for me. It's doable on your own, but if you think it'll be big, hire a lawyer to do it right (and, more importantly, fight the patent office if/when they initially deny it to get it accepted).
It may be the way to go for you. Consult a lawyer, this is not legal advice, YMMV, etc.