This is copied and pasted from the Degiro website. I Phoned for them to confirm these fees as well. The exchange rate that they use is the exact current exchange rate !!
"FOREIGN CURRENCY
A. All foreign currencies via a manual trade € 10.00 + 0.02%
B. All foreign currencies via Auto FX trader 0.10% *
* processed in buy/sell price at time of execution"
A. Is relevant if you intend to purchase a foreign share.
B. would be for frequent trades OR if you just wish to use this service to exchange currency.
This option seems incredibly cheap.