He meant Pre-War money, which is economically unaccepted by other settlements now.
Well, it's worth a lot less than even say, the NCR money, but I never noticed anyone complain when I pay them using a wad of pre-war bills.
I've often tried to compute the value of a single pre war dollar, but the estimate ends up being different every time because it's impossible to know exactly how many bills are in each wad, and what they are valued at.
Then again, it might be that since the money lost its government backed value, that a 20 dollar bill is equal to a 1 dollar bill.
Of course, people might again be conscious of the face value of prewar money considering that NCR money is so similar.