Another discussion about how much to charge for creative work here.
Keep in mind that your day- or hourly- rate is your minimum—it’s what you need to make in order to survive. What you charge may exceed your rate. It’s not how much your overhead costs, it’s what you can negotiate.
For more info on what graphic artists are charging, take a look at the Graphic Artists’ Guild’s Pricing & Ethical Guidelines.
Best of luck!