High customization is a bit more complicated. Advances in t-shirt tech have created more choice for customers, and it's harder for producers to keep up with demand. Here are some of the customizable t-shirt elements that drive up costs:
Firstly, not all t-shirt materials are the same. Cotton based shirts used to be the only option for custom prints, but now tri-blend and performance shirts are also popular options. Cotton shirts tend to be rougher on the skin, but more durable and cheaper. Tri-blend shirts are softer and higher quality, but more expensive. Performance shirts are the most complex, with special sweat-wicking and UV blocking materials available for athletes. While shirt composition isn't the main factor in t-shirt cost, it is an important consideration.
Printing methods vary as well. Most companies use screen printing, where colors are added one at a time to a batch of shirts. It sounds simple and cost-effective, but the issue with screen printing is location; shirts must be transferred to a new station for each color, complicating the printing process and increasing imprinting time. Other methods include DTG (which shoots jets of ink at a blank shirt), heat transfer (where heat is used to transfer a design), sublimination (a higher quality, but more expensive variant of heat transfer) and embroidery. Regardless of the printing method, this is the step that typically contributes most to the t-shirt price tag.
Location prints involve printing on areas usually inaccessible by a screen printer, like the shoulders, sides, and top of the shirt. Most companies and customers shy away from location prints due to excessive cost, though, so you likely won't encounter location printing fees.
Lastly, delivery speed can add on a hefty sum. Even for companies that advertise a "no shipping costs" policy, rest assured that those costs have been distributed into other add-ons instead.
Now that you have a window into production costs, take an extra second to think before you order a batch of custom t-shirts. If you're looking for low priced, quality shirts, you'll be hard pressed (pun intended) to find some.