Now that almost everyone has a flat pocket-computer, it should be much easier...as the Euro and the dollar collapse into nothing.Looking at those price tags reminds me of my trip to Europe when every country had its own currency and I had to mentally figure what that numeric figure meant in actual money.
It shouldn't be hard to make an app do it - enter a currency, or two currencies, and the app uses spot values on each to get an accurate conversion rate.
At least then, you know what the banks or exchange counters, are ripping you off for.