This question might have been to me - I try only to buy reasonably ethically made clothing, and figure on paying up to a 50% or so premium for it. I buy a lot of Patagonia and Ibex, but dress shirts are a problem (suits would be too, but luckily I don't have to deal with that very often). I do think that new models of manufacturing have the potential to ameliorate some of the ethical problems as well, by shrinking the supply chain back down so that retailers actually have some idea of what's going on in their factories. Everlane is an example of what I'm thinking about, but I didn't love the shirt I ordered from there, and they only have S/M/L sizing.
How much more would you pay? 10% 20%?