I strongly believe that the bubble is going to explode soon and when it does, those graphic cards will go straight back to the market as used cards and the prices of both new and used ones will fall considerably.
Its not just Nvidia cards, but also ATI cards. All RX 560, 570, and 580 are out of stock right now. I barely got my RX 580 for about $300 which is $50 over MSRP but now they are selling for over $400 now. I think it will be like this for another year or so, or unless the bitcoin crazy bubble burst. Hope it will be soon.