I spent a lot of money for a helmet ... once. It seems to me that bici helmets are like champagne ... you do get what you pay for, but the price goes up exponentially in relation to the comfort. That's just my experience, but I'm back down into the $60-70 range and that's plenty comfortable for me. The difference I notice in hot weather is pretty slight. I overheat fairly easily, and doing the normal things like getting ice when I can, soaking my hair whenever I stop for water, keeping a bottle of plain water that I can squirt down my back and/or into my helmet, unzipping my jersey as far as it will go and dealing with it flapping in the wind - all that makes much more difference in cooling than the helmet, IME. Just my opinion though, I know some people really swear by the honeycombed helmets.