What you'll get is a hand-drawn piece of artwork, on paper, and then that artwork will be transferred, also by hand, to a t-shirt. Because I'm doing everything by hand with dyes etc, there's a lot more that can be done than a t-shirt printer can offer; for example, designs on the sides, up around the neck, on the sleeves, and so on. Some colour can be put on too, and even glow-in-the-dark, if you like.
This is what I have done so far, to give you an idea.

As a base price, the top left one (the AMG) would be about £12, and prices will go upwards from there, depending on t-shirt colour, how much dye I'd use and how much of the t-shirt is covered, additional colours, etcetera. This is just to cover costs and no more, really. The t-shirts are brand new and will have never been worn, and the artwork alone is something I'd normally charge around £20 for, even without a t-shirt. This will be a fairly limited thing, maybe only five or six, but I will always offer Zoners discounts on stuff, and for every one I sell, I'll be donating 50p to the Zone.
With regards to washing and general wearing, I can't offer too much official guarantee yet, but I've found them to be very good at surviving. The colourful tiger t-shirt above is now well over a year old, and has survived many raves and club nights, lots of wearing, and probably 50+ washes. Cold wash is obviously recommended, especially for colours, but the black lines will last through pretty much anything.
Feel free to discuss ideas with me. Thanks!