How much money would it take to bribe the majority of miners to attack the system? I think this question is just a re-formulation of the 51% attack, but it has me thinking: miners are monetarily incentivized to not perform a 51% attack, but there must be some amount of money will cause their incentives to switch. So how much is it?

It is commonly understood that miners have invested in equipment, and so doing something to harm the value of the cryptocurrency they're mining (ie, engaging in a 51% attack), undermines their investment.

But what if a very wealthy entity bribed the miners, external to the bitcoin system, with an amount that exceeds any returns the miners could possibly hope for? For example: a govt pays a majority group of miners $X billion + electricity costs to just 51% attack the network with empty blocks indefinitely. 

I think an attack like this could be effective in hurting the public confidence and price, but there are ways it could be thwarted too (switching the POW algorithm, for example). So I don't think it is dangerous in a fatal way. 

So my question is: can we estimate how much money it would take to successfully attack the network in this way? 

Cost of attack = [(51% of block reward + fees per year)-(cost of 51% of equipment purchased for the next year)-(51% of the network's electricity costs for the next year)] * (number of years worth of income it takes to bribe the miners?)

Am I missing anything here? Or making false assumptions? Interested to hear what others think
In a parallel thread on "https://bitcointalk.org/index.php?topic=2512771.0" I didn't do the exact math, but a rough calculation shows this:

Currently there is a hashing power of the equivalent to roughly 800.000 mining boxes type "AntMiner S9". For a 51% attack you'd need to buy 400.000 + 1, and bring them on the network (their power cosumption is 1200W, so you'd need a coal or gas power plant, industrial grade level). If you want to "buy" the miners (bribe), then it requires a lot of communication to them, and a financial incentive. Would the miners follow the fork (bribe), if they can see, that they will loose the value of the bitcoins to be mined? I mean, after such an attack would have worked out, the value of bitcoin would run against zero (quickly). What is the remaining incentive for a miner?
Your one-time bribe would maybe need to be equivalent to maybe a 1 year income of a miner, and this for 51% of the miners. Currently a 12,5BTC reward is ~10.000 EURO/CHF/USD, 6 per hour, 21 per day is 18mio a day. And you need 51% of miners. Big gee ...