Some background on the cost/value of gold and fiat currencies.

In a world with multiple fiat moneys, the zero value of money equilibrium lurks for each of the fiat currencies, including gold.  Admittedly, as regards gold, so far so good.  Gold has positive value.  It has had positive value for nigh-on 6000 years.  That must make it the longest-lasting bubble in human history.

http://blogs.ft.com/maverecon/2009/11/gold-a-six-thousand-year-old-bubble/