I took some chunks out of the back of my old helmet in a crash and need to replace it, but don't have much money right now. I've found some helmets for $20 that say they meet DOT regulations, but don't really know what this means and I really don't think I would trust a $20 helmet. I also see helmets going for $300+ but don't want to spend that much. What is a good helmet for a good price?