Was £100, was £80, now £60
£5 unlock available on eBay
The further £15 discount with groceries offer to bring the price down to £45 has been reported as still working today (Thurs 20th) at the till, although the signs reportedly say the offer was supposed to be only until 19th September.
See previous thread for more details:
This phone's forum on Modaco for rooting/custom roms etc:
Install official ICS / custom ROM from scratch: http://huaweig300.com/huawei-g300-install-a-custom-jelly-bean-ics-rom-from-scratch/