Some Credit Card (C/C) issuers charge up to four percent "foreign currency transaction fee." I posted some info on this many moons ago. If you can contact the correct person at Customer Services for your C/C you can get the rate your C/C addds on. That, in itself (i.e., finding someone who knows what you're talking about) is a challenge.

I personally use a Credit Union ATM Card (no transaction fee) to withdraw cash and pay cash for as much as possible. That's easier now - with the Euro.