My favourite t-shirt of all time was a picture of John Lennon and underneath 'all you need is love'. It faded over time so I threw it out, but people still have a really strong connection to wearing t-shirts that actually mean something to them.
Give it a go. Design your line (be wary of copyright and royalties for images and song quotes, etc), get your image templates together, find a t-shirt factory in china and have them stencil the images on. Only buy one sample of each shirt though. It might cost you an arm and a leg for such a low quantity (and they charge a 'template' fee for the first one you do), but better than losing thousands and having tons of stock if you get stuck in the future.
Create a niche webiste, have professional photos taken of each of your t-shirts and upload them. Set yourself a reasonable delivery date to customers, and see if the chinese factory will "drop-ship" the product for you (direct to the customer). You will be working with 0 profit to begin with because you may charge $20 per t-shirt and the factory will charge you $20 to make a single shirt and ship it. Calculate how long you can operate at 0 profit until you have sufficient quantities to reduce your buy price from the factory. For example, an order of 5000 might bring each t-shirt down to $5.
Not sure whereabouts you live, but you could source local printing companies (and buy the t-shirts locally), but the designs on the front would have to be spectacular (so you can charge enough per unit to still make a profit).
As with any product business, the more you make / buy - the cheaper they get and the more profit you make.
Best of luck!
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