I usually respond by asking them what is backing the dollar.

Sometimes they say gold, which is always funny to me.

"The dollar is not backed by gold, it's backed by bonds. In other words debt, but even if it was backed by gold, what is backing gold?"

Ultimately I get to the part where I tell them all value is subjective. Neoliberals have a pretty easy time connecting with that.

It can be starting point.