There are many perfectly good helmets under $500, and even more under $1,000. But, those price ranges normally equate with higher quality helmets providing better ventilation, quieter helmets, better range of vision, and some other cool features like visors, modular chins, Bluetooth compatibility, exotic composites, etc.
A helmet MUST fit. Then find the features and price range suited to your needs. You need to wear a helmet, and a heavy, I’ll-fitting helmet is neither safe, nor fun to wear.