I used holidayphone.com. They have pre-activated SFR SIMs for 3-days of use for $21 each. I believe these are data-only.

I bought 2 for $42 and they didn't charge shipping (otherwise they would have for only one SIM). They shipped it out of Sweden.

So I used these two for a week trip to Cote d'Azur. I didn't have great reception at my Cannes hotel (though reception in Cannes in general was fine).

Used it in a Mifi and the data was suppose to be unlimited but didn't come close to using a lot of data.

Reception and speed was fine when I used it on a train from Cannes to Monaco.