Clearly explaining the concept of "normalizing" price and relative prices to undergraduate
I usually ask if they would rather get an IPhone or 5000 South African Rands (ZAR). You can also ask if 5000 ZAR is a good enough monthly salary. As we are far from that country usually no one has a clue about the currency exchange rate.  This way you can explain that the number in itself is meaningless, what matters is what you can exchange it for, i.e. relative prices matter.