You haven't mentioned what carrier you are with currently. Some have decent rates for calls to Europe. I have a Prepaid Red Pocket Annual sim that has free calls to Europe and other locations. It is only $99 a year and gives me 1000 US minutes, unlimited texting and 1Gb of data per month for a full 360 days. No calling from outside the US however. My cable provider charges $.08 a minute for calls to most Euro countries with my bundled phone service. Ironically, T-Mobile charges $.25 a minute to call the US from Europe, but $3.00 a minute to call Europe from the US!

Probably time for a little research in to what you may already have available.