Diana,
Not to sound like a smart axx but are you being a sponsor of the event or you coming at this from a business aspect where profit is important?
We just finished a similar order for a transplant patient we sponsored 30 shirts and the remainder they paid for, total order was around 60 shirts, while we didn't make a dime on the job our costs were covered and everyone was happy.
But to answer your question from a business perspective about $9 a shirt would be a fair price to sell them retail, if you wanted to give them a discount you would have to decide what you want for your time and expenses.
Hope this helps