mpspeedy's estimate is a pretty good one I would say, if you are making it to earn at least a little something for your time and skills. If you are doing it as a labor of love for a friend, that's a different ball game. But then, if other family members want one, can you cut them the same deal you did for your friend? Just noticed you said co-worker, maybe you aren't that close, so then set a price with the idea that you may be making four. How badly do you want to be making shirt quilts for the next ?? months? Charge enough to make it worth your time and effort. I don't think people who've never made a quilt realize all that goes into it!