Bitcoin mining cost was a lot more than current price but when price went down the miners stopped mining (some of them) and the difficulty dropped as well which made the mining cost a lot less. Hence we can see from that bitcoin cost is not the true price. It is only backed by people and people who think bitcoin worth a certain amount, sort of an agreement between buyers and sellers which changes constantly. As long as we do not turn into some sort of stable coin (impossible) price will keep on changing.