Hi,
Just to echo what has been said, i found the French orange 3g sim quite expensive two years ago - it would have been ok just for email, but the kids always streamed video!
I think from memory i paid 15euro for the sim, and topped up 15euro for about 3 hours useage - i couldn't work out the data allowance and they only talked in hr / min on the leaflet.
Last year we just used free WiFi (paid a few euros once, as we needed to skype at a certain time).
I have purchased a wifi booster this year - had some good results in the UK
Cheers
Matthew