6.2 billion. Meh. That means anyone in the Forbes Top 50 could take it down whenever they want?
Around 6.3 billion without electricity cost (Around 3.9 millions $ per day - you imagine the power of eletricity required and how to get all that amount of antminer ? they must have their own power stations, and try to buy the plan of antminers and build them self as one user suggested above).
As I already poited out in another similar puffy topic, there is no need to spend zillions of dollars for that (and then wait for delivery infinitly).
It's enough to pay much less to one or two biggest pool admin(s) for modifying their software (and you will get the entire hashpower immediately as a bonus).
Additional bonus for pool (i.e. miners) shall be a reward for all the 'overmined' (overriden) blocks.
We already know this ... i just wanted to make the calculation to exploit this side too.