I'm not sure about cost of living differences between Michigan and the Baltimore/DC area (where I am), but I think that they are higher here so I guess that should be taken into account.
When I freelance, I bill a flat rate $50 an hour. I don't charge for copies, faxes, mileage or long distance calls if necessary, although I do itemize on the bill because the layman doesn't really understand exactly what he's paying for (they tend to think mentions just magically appear in the newspaper! lol)
But like I mentioned, you might want to adjust this fee based on cost of living.
I think you'll enjoy freelancing! It's not a pressure cooker like corporate PR and there's something relaxing about sitting in your own study typing a press release in your pajamas!
Good luck!!!