lol typical salesman reply...
You'll likely find that the main difference between a helmet that costs a few hundred and one that costs $1200+ are things like air vents, snazzy colour schemes, racer endorsements and the like. You'll also pay more for removable linings (so you can wash or replace them as needed), clip-in guards that deflect your breath away from the visor, different kinds of visor pods, and of course the brand. HJC for example will always be cheaper than a Shoei or Arai. It depends just as much on what you're planning on doing with it as anything else.
All that said, if the helmet isn't comfortable and/or doesn't fit you properly, it's not safe. If you have a fat head like mine you'll probably want to look at a HJC, they're middle-of-the-road stuff in terms of features but just as safe as anything else. Remember that they all have to pass the same standards, but some pass by a much greater margin than others All helmets sold here should be ADR approved to the best of my knowledge, but some will have other endorsements such as SNELL.