Helmet rule. Purchase a helmet that costs at least what you think your heads estimated value is.
If you think your heads value is $80 or less then a sub $80 helmet will be fine. My heads value is at least $750,000 cause thats what my health insurance spent to remove a brain tumor. I purchase nice helmets but can't fine any that cost anywhere near the value of my head so I consider all of them to be cheap no matter what they cost.