For me, $100 is the sweet spot for helmets. Little lighter, better ventilation, and a better fit than the $35. What the extra $100 buys isn't that big a concern for me. If you know your helmet size, you can often find helmets in the $175 range discounted to around $100 online.

One thing I didn't touch on before is wind noise. Cheaper helmets also tend to be noisier.