...and took it to my local screenprinting shop, who will print it up over the next couple of weeks. My plan is to see how they do with this job. If I like the results, I'll ask the shop to print my subsequent designs as well. The shop is within a few blocks of where I live, and is owned by a local family, so I hope to be able to partner with them going forward.
By ordering a batch of 120 shirts, I pushed the per-shirt price for this order down to the lowest level the shop offers. Overall, I'm getting 120 white t-shirts - 60 XL, 40 L, 10 M, 10 XXL - with the design on front and my logo on back for about $700. The cost would go up if I wanted to print on a colored shirt or if my design used more than one color of ink.