In the US, there is two ratings. DOT and Snell. For a DOT rating, the manufacturer submits a helmet they select for testing. Once the one helmet has passed then the entire line is qualified for a DOT sticker. Full coverage DOT rated helmets can be purchased for less than $100 and up. Imho, they are perfect for keeping rain and bugs out of your eyes. For a Snell rating, Snell goes to a retailer and takes one off the shelf for extensive testing. All major US racing originations require a Snell rating or the European FIA rating.
Btw, I raced Sprint cars and Midgets for over 20 years.