Hi Daniel.
You can solve your task in 2 ways:
1) Use AJAX to call some remote service that will give you required info (exchange rates in your case)
2) Use Velocity to call some your local service that will provide the required info, like this:
1 #set ($currencyLocalService = $serviceLocator.findService("com.daniel.service.CurrencyLocalService"))
2 #set ($rate = $currencyLocalService.getExchangeRate(someDate, currencyAId, CurrencyBId))
And then use $rate variable.
