As the investigators travel across Europe, its likely that they'll have to exchange moneys. Today, we're used to the idea of Europe using a unified currency - the Euro. In the past, it wasnt so easy. The British have the Pound Sterling, the French use Francs, Italians are all about their Lira, the Germans are struggling with massive inflation and the Reichsmark.
Well..... heres a copy of Guttags Foreign Currency and Exchange Guide. It has far more information about monetary exchange rates than any investigator or keeper are likely to ever need. So it might prove to be a handy resource.
Guttags Foreign Currency and Exchange Guide
Something for Investigators and Keepers to keep in mind, the book is just a guide. Local exchange rates may vary wildly, and public perception about government stability may lead to people using entirely different rates because of a preference for a more stable currency (Example: In Italy, the 'official' exchange rate between a dollar and a lira might be about $0.20 for 1 lira, or 5 lira for a dollar, but the unofficial exchange rate might be 10 lira for a dollar, because the Dollar is perceived to be a more stable currency).