Producing a monetary commodity is the same kind of activity as any other, and it entails costs. Scarcity is one of the reasons why a particular commodity becomes money at a given time and place. In practice, this usually means that the costs of producing money are quite high. Conversely, one of the reasons why a commodity ceases to perform the monetary function is changes in labor productivity—technological advances, and so on—that make it possible to produce money in larger quantities. For instance, it turned out that iron was not suitable for the role of money, since its reserves are quite large, and at a certain level of technology it can be produced in considerable quantities.
What matters is not the quantity of money per se, but the speed at which its supply can be increased. When the money supply changes rapidly, the price structure becomes distorted—not due to shifts in supply and demand, but due to monetary factors. This leads to chaos, and if it continues for long enough, the market begins looking for another commodity to serve as money.
Even modern governments, which produce money at virtually no cost, nevertheless try to keep themselves in check and avoid crossing a certain line—unknown to anyone—beyond which lies “hyperinflation”: a situation where the public, even under decreed money, seeks other means of exchange and abandons the “national currency.”