The main reason to buy $200+ shirts is fabric or design details.
Designers often have fabrics woven specifically for them. A mill will not make the same fabric for someone else. Etro and turnbull do very special looks. there is no way that I can get the exact same fabrics.
There are also inticate design details that might be diffiicult to duplicate.
My basic shirt is just that. a simple shirt made to your measurements with the various details that can be selected.
I can duplicate crazy details. These are no longer basic shirts. The price is much higher. I am making samples for a very fashionable NYC clothing company. The details are driving us crazy, but we can do it. They are also willing to pay for these details. Eventually the production will be made in India where those details will be inexpensive to reproduce.