I've never had t-shirts printed and can't reccomend any company that does it.
I would think familiarizing yourself with the types of t-shirts availible would be the first step. Heavy cotton, pre-shrunk, mixed fabrics.
Then realizing what type of price your after. Then look at what you want printed. Then look at what you get for the money.
It's not that hard to print your own shirts. This is what I would consider being a "homebrewer". Especially if you are going with a single ink color.
You need the shirts. a stencil of what you want to print. Some decent ink with a way to apply it, perhaps either air brush, or regular brush.