^I should add that the more expensive helmets get does not mean they are more safe. A cheap helmet is just as safe as an expensive one, but the expensive helmet might do it in a lower profile (because of more expensive materials for example). So, when you pay more you get a helmet that is just as safe, but a better overall design- lower profile, lighter weight, more adjustments (usually). But I still maintain that a helmet that fits better will protect better than a helmet that does not fit.
My weird head is a perfect example. Lots of fancy, expensive helmets just don't fit my head but I found a rather "basic" helmet that fits me like a gem. I wish it were made of carbon fiber and diamonds but the truth is they all are rated for one impact, and I tend to fall a lot. So that means I need to replace my helmet more frequently and it sucks to have to keep doing that with a 200+ euro helmet. This summer, my roommate crashed his brand new carbon fiber TLD D3 the first week he got it. He was in tears not because of the fall but because he had to go buy a new $500 helmet to replace his now expired one. So, it also depends on what you feel comfortable spending and re-spending.