Mailing your idea to yourself won't do you much good. I believe it may work for something like song lyrics, but not patents. If you reveal your idea to anyone before you apply for the patent it's fair game for anyone to patent it.
Having a lawyer take care of it can run at least $10K depending on how much work they have to do. If you can take care of drawings and basic content of the idea (description, applications, etc) to the point where the lawyer only has to define the claims it will cost significantly less.
