It seems to me that you get what you pay for (extra cost = better ventilation/removable linings/chin-strap fasteners/pinlock/breath guards/general quality feel etc etc) BUT those extras are very expensive. You'll probably notice the difference between a £100 and a £400 helmet, but it's less certain whether you'll think that the difference is worth £300. Like Techno said you can just go for an older model. I got a Shoei xr1000 for about £250 (first one i tried on and it fitted PERFECTLY). When they were the current model they were over £400 or something stupid. THis year at NEC show they were down to about £190 i think. But i've seen loads of cheaper ones which look perfectly fine assuming they fit properly, and they all have to meet the safety standards. If I was a bit tight for cash and buying gear then i'd go for a cheaper, but good fitting, helmet and then spend the difference on proper boots, etc (places people skimp on or delay), where the cash would go towards proper protection rather than reducing wind noise and the like.