I am staying in France for 3 months and I am looking to buy a Pay n Go simcard for my old 2.5G iPhone which I have unlocked and jailbroken on 2.0

I am looking for minimal cost, a small amount of voice minutes/texts but a high amount of data transfer...... my intention is to tether my iPhone to my laptop to use the internet and although I am only going to be browsing and not downloading any files, it will still use a significant amount of data so I need a deal with lots of cheap data.

Anyone know what the best deal is?