Audition to work with a local theater group. When you're ready to market yourself, go to a professional studio and have a quality demo tape assembled. If you're a beginner, you'll need to do some mock commercials. Get a pro to help you with this. If you hire an agent, they'll probably help distribute the tape for you.
Some performers join unions.
In that case the Union will tell you the minimum to charge. I honestly have no advice for you on that one other than to maintain your tenacity. Keep crossing the desk of the producers and maybe they'll hire you. That doesn't mean call them every week or even every month. Send your initial demo tape and then follow up with a postcard or letter every couple of months.