I believe that the paper the government has to print them on is getting more and more expensive
What makes you think that? Google "cost of printing money":
$1 and $2: 5.5 cents per note
$5: 10.9 cents per note
$10: 9.9 cents per note
$20 and $50: 10.6 cents per note
so it's getting harder for governments to print currency
If I could print 471 $50 notes by paying 1 $50 note that seems like a very cheap way of creating more money!
and manipulate the currency supply.
The FED doesn't need to print money to do this. They just adjust the interest a bit and punch some numbers into a computer.