I'm a Canadian and I spent $800 CAN on an equivalent brand. Yes that's expensive but I will probably never have to buy another winter coat as long as I live. I bought it specifically when I saw someone complain in a review that it kept them too warm.
Even if I only face a few days at -20 degrees weather, it can keep me alive, if the public transit system breaks down, or if I have a reason to be outside of the city in winter, and of course, comfort. Some years there are prolonged cold snaps. And I get cold. The coat is good for -40 degrees, but probably only for "normal" people. Skinny people like me need a heavier coat.
I thought Mustachianism wasn't about not spending money at all, but about spending money only on things that are important or necessary. If someone is buying a heavy winter coat just for the sake of fashion, that is anti-mustachian behavior, but I wouldn't attack the coats themselves. (I'll be happy to tell you my coat is not fashionable. Frankly, I had hoped it would be fatter. I wouldn't mind looking like the Michelin Man. I'm interested in warmth, not "looking trim".)
I could have bought a musk ox underwool sweater for $4,000. That would also keep me warm, but unlike the coat, you can't wear it day after day, and also... it costs five times as much. (Also not fashionable, not that I care about that.)