I'm sorry to make this question, I'm very new to bitcoin but I need to ask: Wouldn't buying common stuff like bitcoin be extremely hard and volatile?

Lets make up a city where bitcoin is the official currency, in this town, there are regular shops like coffeeshops and stuff. Lets say that the value in the coffee is 0.00003 bitcoins. How would I know if that is expensive or not?

From what I've learned so far, it's an extremely well-fitted coin. It's safe, it's hard to make more, no one controls it, but why does the value have to be this BS number crunch? If I saw the same model of car, but in different use conditions, one costing 0.003 and one costing 0.0031 how would I know if the difference is worth it?

Edit 1: Sorry for the title, I meant "Buying stuff WITH bitcoin"