In the year 1900 AD, $1 USD is equivalent to ~$30 USD of today.
So ~130 years ago it was worth 30 times as much. That’s a rate of roughly 23 times more valuable per century you go back. There have been 20 centuries since the year 0. So 20*23 = 460 times as valuable.
460*$47= $21620 of today’s money. In other words, yes, that’s pretty low for a copay in the US.