Well, there are certainly places where cheap Chinese knock-offs can come in handy but when it comes protecting your head, I would highly recommend staying away from cheap crap.

I recently picked up an Omne Air Spin for $150 and it's honestly one of the best fitting helmets I've ever had. There are several lighter and more expensive ones sitting on my shelf at home but I always grab the POC for some reason.
My last crash saw my trusty Giro split in 3 pieces but, I walked away with nothing more than a serious case of road rash. Pretty sure I'd be drinking my remaining meals through a straw had I been wearing some cheap knock-off instead of a well designed piece of safety equipment.
Just my humble opinion....