Cost of harwares:
Hardware = Current hashrate * Price of Antminer S9 / Hash produced by Antminer (per seconds)
Hardware = 36349358,259 * 2400$ / 14
Hardware ~= 6,231,318,559 $
This is one time investment.
So attacker have to pay 3,855,627 $ of electricity per day !
And this is what the attacker would have to pay every day if they wanted to keep the attack alive.
With so much money involved I guess this could be pulled off only by the government (if we don't consider the most important miners currently mining bitcoin). Which would be hard to maintain long term, as the government presumably wouldn't be making any profit out of it. Also knowing that if they somehow managed to destroy bitcoin, there would be numerous other altcoins waiting to take its place, so it wouldn't be worth even contemplating.