The higher price might buy less weight, better finish, more comfort and features ect.
Less weight is more safety. Think about what the effect is of having a weight attached to the end of your neck in a crash.
Also, those helmets might have passed the same safety standards but that does not indicate that they are of equal quality.
6D helmets, Kali, POC, Smith and Bell all have designs that are aimed at going beyond the basic standards by lowering the chances of sustaining a concussion. Which companies design is the best is anyones guess though.
If I was going to be buying a full face right now, it would be between a Kali and a 6D. If I was after a half lid, it would be between a Smith and a 6D.