How much should i charge for my design services?

I'm a technical writing student, and as a project i did a brochure for a restaraunt in my community. I did it for free, because i the guy who owns it is pretty chill, i was getting credit for it, and it was also my first. Well now word has gotten out around town, and i have a couple projects line up for me. The thing is, most are beginning businesses, so i'm not sure what is a fair price for my services. I don't just throw a bunch of pictures and text together and call it an ad. I design my own templates, do some photo editting, research the area, because a lot of these businesses are in the historic area. All in all i would say i could spend a full days work dedicated to the project.