do you want print on them? If so I can get you wholesale. email me firstname.lastname@example.org
T-shirt printing or silkscreening allows you to get the same image over and over again and the same colour over and over again. It also speeds up the production time compared to if you were going to do the shirts yourself. By the time you design 1 T-shirt in one hour, 200 could be done on the press (depending on the business.).
It is cheaper if you order by bulk - the more you buy or do, the cheaper your shirts get. For example, one or two shirts might cost you $5.00 but 100 shirts might cost you only $2-3 each.
To paint on the shirt will take time and so you have to ask yourself what your time is worth. You could create a painting and then have it transfered to a shirt using the silkscreen processs.
Silkscreen shirts also seem to last longer when you wash it than an original painted on shirt.