Coffee Catering, what to charge??

[mcohveca]

We have partnered with a restaurant in our area which often takes on catering jobs and I am not sure what to charge. Would you estimate by number of people attending the event and determine a dolloar amount per head? That is what I have used so far, but I'm not sure what to charge. We are not serving espresso drinks yet, just brewed coffee.
Any suggestions?
Thanks,
Alex