Reddit mentions of 3M Speedglas 9100 Welding Headband 06-0400-51/37179(AAD), Assembled Parts

Right, so here's why I think it can (easily) be under $50.

Rigid headband (cheapest)

"But they show something padded and custom and black!"

Right, so look at this. Lots more plastic bits, including ratchets for the mask, and it costs drumroll $3 more. The second headstrap is also far more complex to assemble. This specific iteration of welding head mount probably moves fewer units than the Vive will, so the costs are the same. At most, the extra 'fluff' on the vive headstrap is worth, to manufacture and assemble, under $20. The headphones could add a good bit of change, but the head strap itself simply will not cost HTC more than $20 to manufacture and ship to the US. It just won't {again, not including cost of headphones because we know literally nothing about them}. The cost of this headstrap is purely down to how much profit HTC wants, and how much they have to give Valve and whomever else in royalties.

tl;dr: I'm not saying because one head strap retails for $15 or $20 then HTC only costs X to manufacture. I'm arguing that because there is a $3 price difference for a far more complicated headstrap, the true manufacturing cost difference is likely in the $1-3 range. I have no idea how much either strap costs to make, but I know one probably costs $3 more, at most, than the other, to manufacture.