Here are the major factors in the price of tee shirts and screen printing.
Shirt Color
White shirts cost less than colored shirts. Imprinting on white shirts costs less. Imprinting on mid-tone and dark shirts costs more.
Number of Shirts and Imprints
Simple enough. The more shirts, the lower the price per shirt.
The more imprints per shirt (chest, sleeve, back), the higher the price per shirt.
Number of Colors In Each Imprint
A simple logo can be imprinted with one color. Complex logos may require two or more colors. Pictures and colorful illustrations require full color printing.
One-color printing comes with the best price. Additional colors cost more.
Artwork
For best-price one-color imprinting, vector files can be set up more easily than JPG and other non-vector files. The same applies to 2-color and more.
For full-color photographic printing, vector files or clean, high-resolution JPGs usually work.
If the files are not to specification, artwork prep charges can apply.