Totally agree. It's cheaper now to buy a full size sim and a micro cutter but even the full size sims have gone up from £11 to over £15.
As I'm not a heavy data user, I have started using Samba Mobile which also uses the Three network. You have to watch adverts periodically (but totally independantly) to build up free data "airtime," Get a friend to recommend one and it'll only cost £2.50 for the sim. They periodically have double or treble data weekends.