Buy the helmet you know you will wear and feel good in both looks and comfort...regardless of price.
If it's a $25 helmet, then good....if it's a $200+ helmet, then good.
I bought a Catlike Whisper off ebay for well under $200 and for my head, it's the best fitting helmet and looks good.
Initially, I couldn't justify a Catlike...but then I went through several cheaper helmets that never felt quite right and didn't like wearing them.
It was definitely worth it to me.