When I purchase items for a Zynga game, you can see the price in local currency. What Facebook APIs can be used to determine the price? Can I get the price of credits in either local currency or US dollars? Example below.
10 credits = 1 USD
Use an external service for getting current exchange rates for other currencies.
I have used the free XML file from the European Central Bank in the past, but that's based on the Euro (and up to 1 day old). There's probably lots of other sources available online.
You could just google "13 USD in GBP" and fetch the result from there.