I'm coming to London in November for a week with daughter and friend. I'd like to use MiFi adapter (Tether 3G to all 3 of us) and I've searched a bit and found out that GiffGaff would be best but in unlimited data plan, tethering isn't allowed. They do, however, have gigabags which cost £12,5 for 3 Gb. If I buy it with someone recommending me as new user, I'll get £5 and all I have to do is top up with £10 and activate that gigabag.
Is there any cheaper option ?

Or maybe a little bit more expensive, but with more Gb's ?
Thanks in advance.
