Is it something like this you want? click here it says "The Excel function is perfect for whenever you need a currency conversion. I use it to keep track of the British Pound value of a US and Canadian Dollar bank account."
"The rates are scraped from Yahoo Finance, and are real-time (but delayed by 15 or 20 minutes)."
Other than the above, do a google for excel formulas for exchange rate and there's lots to choose from.