Here in Montreal, it seems to me that the difference between a $50 ish helmet and a $100 one is in the mounting hardware, ie more comfortable ratchet system and foam cloth stuff. As someone who rides as soon as ice is gone to when ice appears, a better quality adjustment system is nice because I often change what I wear under the helmet, varying layers etc. Plus a nicer fitting helmet in warm weather is nice too, so worth it to me to spend a bit more.
That said, I don't feel there's any real difference in protection, although I think it's fair to say that a better mounting system that holds the helmet on your head properly better will be an advantage in a crash. I have neighbours who rides with their helmets tilted back poorly on their head, not very effective..... That said, I think most new helmets have reasonably designed rear support systems to hold them in place, even the 35 buck ones, the materials just feel more chintzy, the turning ratchets for example.