Here is a alternate system of coins I worked up for my Mutant Future games to give them a little more sci-fi flavor.
Plastoons (pl)- plastic coins minted by a variety of city-states, not worth much far from originating mints and they can even get you in trouble in areas hostile to the minters.
Lead pieces (lp)- lead coins minted in a number of places. The purity can vary but lead has a low melting point and doesn't draw much radiation so it's possible to tell when too much of the coin mix isn't lead.
Uranium Pices (up)- Uranium coins are the most difficult to forge thanks to the tiny bit of radiation these coins usually carry. Not entirely uranium but if the don't give off enough ticks to someone with a detector the bearer will be in a lot of trouble. Large quantities of the coin are dangerous so the cash keeps flowing and large quatities are often held in lead coffers.
100 pl = 10 lp = 1 up
For Quick pricing of goods simply convert prices listed as cp to pl, sp to lp and gp to up .
If one has coins from fantasy realms turning up in places where folks use plastic, lead and uranium I recommend cp being worth 2 plastoons, sp being worth 1/2 lp, gp being worth 2-5 lp with a charge of 20% or more for money changing the fantasy realms coins.