It all depends on the company (each charges differently). It also depends on the size and location of the printing. Also also depends on the quantity of the order. Buying in bulk always cost less, in the long run.

Questions concerning your order:
1) Where did you order them from
2) Were the graphics original or a combination of generic elements?
3) Was the design(s) printed on both the front, back, and the sleeves?
4) What was the size of the graphics?
5) Were were the shirts made?
6) Were the graphics ironed on or screen printed?
7) Where were the shirts Screen Printed?
8) Would this company manufacturer, screen-print, and then ship each shirt to different customers for you?

A lot of different elements go into providing graphics on clothing. each company has their own methods and limitations. For Example, SpreadShirt will not allow you to put your graphic/logo on the sleeves of a shirt. Instead, they only allow a set of generic shapes. To which you would have to arrange to your liking. Kinda like how Forza allows basic shapes be used to create unigue graphics, but on a much smaller and limited scale. Markiplier has used this method option for his Charity shirts. He used a series of blocks to recreate his logo and arranged hearts around it in a heart shape. RedBubble does not screen print full canvas shirts at all. But they do screen print full canvas Duvets. Threadless does print full canvas shirts, but only in bulk.

For six years, I worked with a small local company that did Iron-Ons at $10 a pop. But in the end, those shirts would just end up fading much faster then screen printing. And in some cases, they would simply start to peel off. If not for labor and product cost, we would have sold them for $5 instead.