Currency is, and always will be, some form of rare substance is Lomeelas. At first it was copper, when copper was first discovered. Then it was crystal, but crystal was soon found to be too...common, in some aspects, and, well, rather useless in others (It's magical properties were not very high). The last sort of currency used in Lomeelas was silver. There were quite a few pros and cons to this substance being used though.
One of the main reasons silver was chosen is that it has high magical properties when used correctly. It is also a means of protection from lycanthropes and mages. This, of course, is also a con. Lycanthropes and mages can't handle silver. At first no one bothered with this problem. Who cared? As long as they weren't a lycanthrope or a mage they had no touble with using silver. Coincidently this was also the period in time in which Lycanthropes were labelled "dangerous" and had to go into hiding on fear of execution. After this period was over people started to realize the problem with silver. The late king in that time quickly remedied the problem with fool's silver, a close cousion to fool's gold.
Fool's silver had no magical properties what-so-ever, but with the right incarnations it could be turned into true silver. It wasn't nescisarilly a rare substance, but it worked, and it was completly harmless to all lycanthropes and mages alike.
Now, after giving you that horribly boring history on Lomeelian currency, I'll try to put it in retrospect for you.
One coin of fool's silver is worth roughly 1/2 and American dollar