Are you near an "EmbroidMe" franchise?
We have done small groups of t-shirts there and it might have been about $15 per shirt - maybe less for printing on both sides. For smaller quanties - they do a transfer, not screen printing. The advantage - you can get multiple colors for no extra cost.
The one time it was "way more" expensive was when we used "glow in the dark paint", because they had to do 2-layers of screens, and it had to be screen printing, due to the glow-in-the -dark.