Important point when buying a helmet, obviously buy it to fit your head but make sure that your goggles fit with the helmet on too or you may end up having to buy a new set of goggles aswell.
I bought a new helmet called "sinner" and some matching goggles, same make from Go Outdoors, helmet £30 and goggles about the same I think. Both fitted like a glove. And I'm very particular, and it has to be right. I think they are great.
Agree totally with Justine, I too bought a Sinner Helmet with matching goggles from Go Outdoors yesterday and all for under £70. The fit is much better than the helmet i bought last year. Sadly for hubby i then needed a matching jacket