What is the quickest way to earn a teaching credential if you already have a bachelors degree?

I am hoping to work as a high school teacher in a private school in California. I have a degree in biomedical illustration and majored in biology as well. I would like to teach as soon as possible and really cannot afford to go back to a university for another long stint.

Is there a way to get the credential without huge expense? I would make a fantastic teacher. :D