[tepmoc]

200K antminter S9 will produce about 50% hashrate of current bitcoin network that cost about 300M$ not counting electricity (200MW). But that means they have to R&D themselves these chips if they want attack quick. Otherwise they won't getting that much hashpower in one piece.

If they decide slowly enter game, attack price will raise significantly since network difficulty will be adjusted as they will add more of their miners into network and their projected 50% hashrate will be just 25%

So realistically its about 1 billion $ to attack current bitcoin network.