In order to accurately calculate a screenprinting product run, you will need to determine and estimate the following as best as possible.

ACost of the item, plus shipping
BCost of the other items to make a print run – film, stencil, ink, etc
CCost for overhead (per/hour amount that pays rent, electricity, water, etc.)
DCost for labour – the time to set up, print, and cleanup a run (per hour amount)
XThe cost for the art – this needs to be considered separately, but it is definitely a consideration. Some of the things to consider about the art include licensing, artist time, and the time for the mechanical art process.
TOTALA + B + C + D + X

Use the following form to aid in your product run calculations.