What is the estimated price of Bitcoin which will push miners to stop mining if its price dropped to uneconomical level?
When a bitcoin was worth less than $10, miners were mining.
When a bitcoin was worth more than $15,000, miners were mining.
The key point is that there is no exact price that would make mining unprofitable. Bitcoin mining is a self-balancing system made up of individuals with different costs, and thus mining is sustainable at any price level.
If the price drops, then the miners who pay the most to mine a coin will become unprofitable, and they may stop mining. But this would only make it easier to mine coins for all the remaining miners, and so the network would find a new balance. A huge drop in price may cause many miners to shut off their rigs, but the disruption to block interval would only be temporary, as the network difficulty would adjust and soon blocks would continue to be found every ~10 mins on average.
In a very extreme case where an extremely significant portion of hashpower dropped off, then the block interval may become extremely long. But a situation like that is unprecedented, and in fact many miners may persevere and mine at a short-term loss, in order to maintain their long-term investment strategy, for ideological reasons, etc.
So TL;DR: the average cost of mining $1 worth of bitcoin will trend towards $1, so a lower BTC price just means that miners as a whole will spend less resources mining bitcoins.
EDIT: To be clear, a price of $0/BTC would in fact be unprofitable to mine, for hopefully obvious reasons. But anything above that will be sustainable.
As long as the price is >0, and subsidy and tx fees>0, mining activity will persist.
Change in price will affect total hashrate as it is a zerosumgame and the total pie just shrunk in value. The global hashrate will simply contract until global reward = mining input (break even).
If subsidy(inflation) reaches zero and TX demand is also 0, then mining will stop irrespective of Bitcoin price, since the reward is null.