Call it apples and oranges if you want, but to me, getting a random shirt from a company I've potentially never heard of isn't so enticing at $23/mo.
That's more than I pay for my VPS, more than I [used to] pay for netflix, more than I pay for a couple of t-shirts I get to choose from woot.
Etc. etc. etc.
My first thought was that you were getting these shirts directly from startups and not making them yourself. Also, agree with $23 being too expensive. $10 would be more in line with what people are willing to pay.
Props to companies like inDinero for sending out free shwag (LOVE the shirt!:])
In Chicago, there are only so many days a year you can comfortably wear a t-shirt out of the house, so unfortunately I'm not your customer. I also don't have $23 a month to throw at simply buying one t-shirt.
However, I may not be in your demographic at all. I haven't bought a shirt in years. I get shirts with fish on them for my birthday from my kids, and Mariners shirts from my family at Christmas - then I collect free shirts here and there. I have zero fashion sense, I wear what people give me, and I hate shopping :)