They are a thing. Find a local tailor. (They often hide out at dry cleaners, but not all of them are good :) OK, that will be more made-to-measure than bespoke - the difference there being that bespoke comes with a master tailor who does a really exhaustive initial consult on what patterns work for you, what fabrics work best, what specific cuts to choose, etc, while m-t-m is more "we measure you, you get a standard tshirt". It'll still be lightyears better than anything you get in a shop.

I'd expect you'll be in the range of $100 per tshirt, +/-

And yes, of course you get to choose a fabric, that's the point of bespoke :) It's also the major cost factor. Depending on your taste, there are some expensive fabrics to have.