It's not exactly a matter of cost. The Vaporflys worn by top competitors are not off-the-shelf Vaporfly Next%, but rather are prototypes that aren't actually available on the market. The new regulations mandate that legal shoes must be on the market for at least six months so that all competitors have access.
Yes, but I don’t believe it specifies how they have to be on the market. I say this because I listened to a running podcast a year or so back when they discussed these in depth, with somebody highly involved in trainer marketing. As long as they allow the public to buy them through a retail channel, I believe it ticks the box. So, they basically stick them on a no name web store, and deliberately describe them badly, so they are nigh on impossible to find to buy, but they are being sold to the public. The podcasters found this out, because somebody bought some random thing from a no name store and “accidentally” got these. The podcast for reference was “Bad Boy Running”, no idea which episode.
They are highly custom shoes for highly competitive athletes and for them to meet regulations they need to be sold (or available at least, as I understand) to the public. Marketing such items, that probably have a very limited usable lifespan, as well as being fairly custom fit, wouldn't make sense to market and sell to the general public. Nike make their real money through said athletes winning major events and the additional value it then adds to their overall brand.
As an aside, the most expensive Nike's sold are the ones they make the least of.
Sometimes, yes. This is common in sneakers. There are lots of limited releases that will retail for < $200, and then fetch thousands in the secondary sneaker market because of rarity.
Getting a new sneaker on drop day is almost impossible. Nike just pulled its inventory from Amazon. They really do make it hard to buy shoes, so they sell fewer, but for oh so much more.