The cost of making bitcoin is not a fixed-dollar amount; there is a feedback mechanism in mining any commodity. As the price of bitcoin increases, new entrants who want to mine bitcoin enter the market, increasing the effort required to mine a bitcoin, as its reward will be shared among a larger group of miners. Similarly, when the price of bitcoin falls and miners exit, the cost of mining decreases. However, the number of miners cannot fall below a certain level, because without the miners providing the computing power to maintain the ledger, the bitcoin blockchain will not remain viable.
If the price of bitcoin falls below its cost of mining, it will quickly go to zero.The real concern is that if the price of bitcoin continues to fall, mining will become infeasible, and without enough participants providing the computing power to record the transactions, the transactions will be infeasible and bitcoin will become worthless.
Eulogy made by Atulya Sarin