Roaming the Globe
The going rate seems to be about $15 a month for an international SIM. That will include the chip, and a few hundred minutes of phone calls. It will typically include about 2~4GB of data. With most plans you can add 4GB data blocks for about $3.
Using an international SIM will usually get you faster speeds, because using your US SIM will usually mean that your data traffic must be hauled back to the US. (Yes, when you are on T-Mobile in France, all of your data first goes back to T-Mobile in the US so they can chose throttle you, and then they route it back to France.)
As I mentioned in another article I am more frequently using the Verizon international program where you pay a flat $10 a day and they treat everything as domestic. (Voice calls, data, everything is as if you were in the US.) But for an extended stay in another country it can still make sense to buy a local SIM.