What is the going rate for a freelance graphic artist?

I am doing a freelance job for a guys starting his own business. He wants me to tell him how much it will cost him for me to do rough idea sketches to start out. then after we brainstorm with those he'll pay me for the finished product. I usually don't do this so I'm not sure what to charge him. I want to tell him what to pay me per step of the design. (note: I have to design several versions for T-shirts, bumper stickers, signs, etc.)