I guess they are technically not middle men because they sit one the start of the value chain, but the company making the t-shirts, the one selling it and the one printing on it are still making good profits. On top of the actual costs of making those printed t-shirts.

I imagine it's not hugely expensive at the volumes bands need, somewhere from $3-10 per t-shirt depending on quality, and maybe double that for hoodies? And if you are buying online shipping and handling, which is another $5-10 that I'm paying and isn't going to the artist. Not a huge deal. But if you don't care about the physical product and just want the band to have some money that's still a good bit of inefficiency