Valid point.
The world back then didn't have an open currency. It was all state controlled.
Discussion
Another interesting argument here is that the stated reason Jesus had Peter pull the coin from the fish's mouth was that -- as the actual property owner -- he did not lawfully owe the tax to begin with.
So then, why did he "pay" it? To avoid "offending them." They had more important work to do than get caught up in a tax revolt. He stayed "on mission."
Even so, read in context, in [Matt. 17:26](https://esv.org/Matt+17.26) he explicitly contrasts paying tribute with being free. The taxed are slaves.