Hmmzz these numbers are very different from the ones I found a few days ago. I don't think they are accurate? It would be too cheap if I follow those numbers on the website you mention. It mentions costs on Bitcoin would be only half a million for an hour, while in practice it is more $100 million per hour...
Let's figure this out, I am curious about the actual costs, maybe it is somewhere in the middle :-)
It seems correct: one hour 51% attack will make you allocate resources that otherwise would mine 6 blocks. 6 x 12.5 x 7500 = 562,500 dollar
But of course this is only the power, it will be extremely hard to set up the hardware