Formula is simple: $/TH * total network TH / total BTC mined
Let's take CoinTerra $3000/TH * 4000TH / 12000000 = $1/BTC, to overtake 51% is not at a forbidden cost.
*sigh*
That's like saying "the total cost of all the gold in the world = the money necessary to hire a fleet of small motor scooters to carry it to my hidden lair".
You are describing a possible, but far from certain attack vector on the network in general, the existence of which might or might not influence the current price (assuming enough traders are aware of it, and agree with your analysis), but concluding that the cost of the (hypothetical) attack sets the upper limit to the total valuation of btc is such a naive view of how markets work (and, as a prerequisite, how the human mind works) that I actually regret bothering and typing up this reply.
Meh.
*posts anyway*