Regarding the helmet: they truly are a no-brainer. Even the cheap 30 buck ones the OP talks about must meet the minimum federal guidelines for safety (in the US). No need for a more expensive helmet, which mainly provide less weight (avoid neck strain over long rides) and better ventilation. Helmets save lives and do not have to look dorky. But you do get a bad case of hat hair.
But I don't think that biking is a particularly dangerous activity. I don't wear a helmet while walking on the street or while driving a car, so why should I wear a helmet when biking?