I have a Three Data sim bought from 7dayshop for £24.99
It is a Micro sim with 12gb for 12 months. Was purchased for my holiday at the end of August, installed in my mifi, connected to my phone then turned off. Wasn't actually used on holiday as the hotel wifi was more than adequate.
So this has 11 months remaining & all of the data allowance minus a couple of MB used for initial setup.
Looking for £15
P&P - £1.50