bitcoin is overrated and overpriced
For now though, yes it is, maybe Bitcoin should go under $100 and stabilize the price. But if it goes too low, the miners will become unprofitable and they will leave.
Miners will leave well before $100
The miners are not needed anyway, since most mining runs through only a few pools. The security the network is only supported by the security of the biggest pools. If the biggest pools, that make up at least 51% together, are compromised, then the integrity of the network is also compromised.
And it doesn't matter how much hashrate is backing those pools.*faceplant*
And of course miners can't switch mining pools

.
EDIT: And whether it cost a billion or a few dollars to create your own mining farm that controls >50 percent of the network doesn't matter at all...