The t shirt business is a little bit like the greeting cards business.
Are you designing  a job for a client, or thinking of making your own line of
shirts?
        There are a few biggie T shirt companies, Harlaquin, Liquid Blue, etc. , and
they have some very fine art.  I have heard that they will buy out a design
for somewhere in the $500 to $1000 range.  Some of their designs are process
printing, but many of the others are 8 to 12 color inks prints!
        What I'm saying is that textile printing is not altogether the same as paper
printing.  I have a six-color press here in the shop, and I do my own shirts
marketed as Geologly Collector's T shirts (which do well in museums, like you
say, the specialty places)
        The nature of puff inks, and printing light colors over dark shirts messes up
anything you've learned about 4 color printing, and the way plastisol inks vs.
water based inks vs. discharge inks work, makes you have to learn a little
more about the textile printing process.  And printing on a ribbed knit
surface means you are printing more on air than on substrate!
        The way many local screen print shops work, or so I've gathered from some of
the trade magazines, is to underprice their artwork in house, to make their
overall bid of the print price more attractive.  But you should have an upper
hand in the quality of the artwork you do in your own studio, over most of the
screen print shops around you.
          Color separations are different too, because of dot gain.  I use Serachrome
Seps in Dallas, and they are pricey but good.  Its an additive color opposed
to subtractive color thing....
        I'll be happy to blabber more if you'd like. There are workshops and videos
for preparing screen print art, and I have the addresses of some if you want
to write me directly.

Darcy