How much should I charge for three t-shirt designs?

I am in talks with someone concerning a potential t-shirt design I will do for them. The person has three different ideas they would like to be brought to life and they have been very good about keeping in touch with me to see what I am thinking. One of the issues they’ve contacted me about is pricing.

This is my first real freelance job since college and I don’t want to blow it by charging too much. It would be really helpful if anyone could throw some figures at me to get my head going. Perhaps even some articles that could help me out. I’d appreciate anything you folks can find.