I like to put special slogans on shirts. For my training stuff, I actually made my own by hand. Used Word to come up with what I wanted, text-wise, printed it on a manilla folder, cut out the letters with a blade, pinned my stencils (including 'o' and 'a' holes, so that it didn't have that 'stenciled' look) to the shirt on a carboard box top, and then used special fabric paint marker.
Came out great. But it was a lot of work. After the third one, I said that's it.
So, recently, I decided to look up online shirt services. Two I came up with seem to have nice product and features. One has more features and seemingly nicer shirt stock, and is twice the price.
For a trial run, I did some simple text on the cheaper site, called
spread shirt. With shipping, it cost about $19 and took about four/five days to get to me. I got it today.
front

back (No, this is no reference to the Queen song. Yes, I have already worn this out.)

I was hoping for an ink, but it's some kind of industrial-grade (I think) decal. I don't know if it breathes. Images, espeically large ones might get hot.
Below is an image of the designer of the other site, called
blue cotton. You have a few options for image designs, as well as uploading your own and how that's considered by the designer. I went for full color to get an idea of a higher-end cost. (Of course this is just the front.) Might be kinda hard to see - it says $29.98, including the shirt, and shipping is free. I don't know what kind of material they use.
