In reply to nough:
Can't recommend a specific model, but if you check the for-sale sub-forum, there have been loads of brilliant sleeping bags sold off for sub £100. I personally would prefer second-hand, but good quality kit, to brand new but not as good quality kit. Don't know if you have any time constraints? But if not and I were you, I'd be sniping the sales for a bargain (eBay can be good too, but you need to be very good at spotting bargains, as there's a lot higher ratio of shite : good stuff on there).