Well, as per me there are two factors basis which price of Bitcoin is getting determined

Supply of Bitcoin is limited to 21 million and yet all bitcoins have not been issued in the market which surges it's price. Apply the logic of price of a Gold here. We know that supply of Gold is controlled by the mining and mainframe Gold trading companies which makes it precious. Further, now when the prices have surged so much. Demand is increasing everyday. Thus, demand and supply mechanism is working effectively.
Second and also an important aspect to this is cost incurred in mining of a Bitcoin. How will this cost be recovered. A massive loss to economies can occur if such cost is not recovered in the system.