You can measure the price of a currency in bread or in screws... How much bread can you get for 15 SATs? I think that's where it eventually goes. The market determines that amount based on the availability of Bitcoin and the availability of bread. A cheaper bread from another supplier drives prices down. A more expensive bread might be purchased because it is more healthy and therefore more valuable. You can measure it in steak or in gold. Its all by the market dynamics.
