Well...
Well, it depends on how fast you are and how much you value this client's continued use of your services.
To design a business card I charge $75 total (usually). It takes me about 15 - 35 minutes for the initial design (based on customer input and what I find out about the type of business/industry being advertised on the card). I factor in about 45 minutes for changes after I present 3 different variations to the client (this includes the time I spend talking to the client). If you get lucky, you present the client with the 3 cards and they say, "I want that one." You have then just spent 20 minutes and made $75.
If the client insists on hourly, I charge a flat $50 hour for graphic design. There are many variables in freelance work; how you are perceived by the client (how professional does he/she seem), have you done solid-looking work in the past and how much do you WANT to do the job being asked of you (if you don't want to, charge more), and how fast can you get a quality design out the door so you can continue reading MacRumors forums
Good luck, hopefully that jumbled mess of words helps you in some way.