Bouygues BandYou prepaid has various recharges of 10€ to 60€. You will need to charge your B&you prepaid upon purchase since it only has 15mins of talk time which does not appear to be useable for normal calls. In terms of data, I believe it is 20mb per € or 0.10€ per minute of call or 0.05€ per SMS. B&you works for me bcos I can decide how much of my credit to spend on data or calls or text. Have not used the data yet so don't know what the speed is.

I don't think orange mobicarte prepaid has data. At least I've never used it with data.

SFR ipad prepaid data is 30€ for 2Gb valid for 30 days. 9€ for 500mb for 7 days. Can't remember how much the data sim costs tho but i think it has 1 or 2 days of unlimited data?

Don't know about tethering.