That grave in Back to the Future Part 3 said something about getting shot over a matter of $80.

$80 face value in double eagles would be worth just over $1200 in 1985 going by the melt value alone (disregarding the historical premium value of the coin).

$80 face value in double eagles would be worth over $10000 today. There’s been more inflation from the 80s to now than there was from the old west to the 80s.

Inflation doesn't need to rise for currency to devalue.