well, if you had a $25 set-up charge, that brings it down to $75. divide that by 12 and your per shirt charge is $6.25. that's fair and reasonable. how i would advertise that is saying your shirts are $6.25 each and somewhere you'd have to say there's a $25 set-up fee.
there are often variables that don't get mentioned in these questions and replies, though, so take that for what it's worth. i promise you someone will do it for $5.
it doesn't matter because the point is your customer, if you talked to them, will tell you they can get it done somewhere else cheaper 87.3% of the time. that's when you tell them to go for it.
but, no, i don't think that's unreasonable. that's close to what i quoted someone not long ago, but my turnaround time is faster than most places. we didn't get the job because the coach over rode the team mom (he didn't want to get *anything*, she wanted to give her girls a little extra something, and gee, i wonder whose pocket that went into? hmmm. lol), not because of the price.
i haven't been doing this very long, but i learned within 6 weeks not to complete with super low prices. i'm not breaking my back for less than i can make working at taco bell and anyone that will can have that kind of work for all i care.