Long story short - high end video cards are used to "mine" cryptocurrency such as Bitcoin and Ethereum.
This has driven up the price of both NVidia and AMD to ridiculous heights.
GTX 1070 Prices Soar Alongside The 'Ethereum' Cryptocurrency
BTW - The prices quoted in the article are already outdated.
Just how ridiculous?
On November 25, 2016, SEVEN MONTHS AGO, I paid $230 for an RX 480 video card with 8GB of DDR5 memory.
Today? - the lowest price that I can find for a new card is $435.
Building a new system? You may want to re-use your old card.