It’s worth remembering that pricing is not just production cost, it needs to consider the cost of research and development, tooling, likely sales numbers, distribution, marketing costs and perhaps most importantly what the market will accept. In some product categories the cost of manufacturing is an almost insignificant part of the final price.
And then there is the fact that designing and building headphones that sound great does not mean you need fancy machining, exotic materials, deluxe packaging etc. There is nothing wrong with those things but if you want them you are paying a lot for style and presentation, not SQ.
Personally I find it hard to justify the prices of expensive headphones. In some cases build doesn’t seem to be that great (for example, the HD650 looks a bit homespun and feels low rent but actual quality seems way better than expensive Audeze models and anything from hifiman). Price is probably the worst indicator of sound quality there is in audio (I much prefer the K712 to the much more expensive K812 for example) and even where they are better gains are marginal and disproportionate to price difference.
Luckily if people want expensive headphones it is usually not that difficult to get them in clearance deals or pre-owned and save loads if you are patient.