If I hypothetically set out to create a single fake one dollar bill that can pass for real ... i would have to spend a lot more than one dollar on the materials ro pull it off, surely?
Granted, a nickel was worth more in the 1930s...but not that much more.
It's illegal to own these counterfeit nickels because it's illegal to own any counterfeit currency, but they pop up from time to time in collector circles. I don't think the Secret Service cares at this point.