It's a very nice development for a person to design his own T-shirt, not a expensive price of 20 dollar, but it caught my attention; Why is not Bitcoin paying?
Dude there are many online logo designers site available in online. If you able to do by own you can only need to spare the money for the printing the t-shirt.
I do not think that it will cost more than 5 USD to print in any photo maker store.
However, if you open a e-store to buy the btc designed t-shirts means you will be able to make more money.