Yep, very nice but pricey I suppose...
I have a low-price HJC (CL-16 (white)) that's served me well but I've never owned a really high quality helmet like SHOEI (and I sort-of want one).
Is the quality really 3-4X better?
I'm actually doing a research project for college right now on motorcycle PPE and this is one of the things I am looking at. Technically, every helmet sold in the U.S. has to pass DOT safety tests before they can be sold. So in that regard, the $600-$800 helmet had to pass the same tests as the $100 helmet did. Crash data is a garbled mess to weed through and most of it simply focuses on whether or not the rider was wearing a helmet at the time of the crash. That said, what data that I can find really doesn't show an increased level of protection from an expensive helmet versus an inexpensive one. The build quality will be better absolutely, but as far as whether or not the expensive one is "safer" or not, it really doesn't seem to be the case.
The major difference I have seen with the more expensive helmets is the materials they use and the major thing is the weight. I picked up a new Shoei (don't remember the model) the other day and I swear it was like holding a few sheets of paper in my hand, it was that light (compared to the $100 Bilt helmet that I'm using now that probably weighs a few pounds). It was also $600, but from the weight alone, I can see where the price comes from. From a safety stand point though, it had to pass the same tests that the cheaper helmets do. There is also SNELL to look at since they have more stringent testing, but it's also voluntary on the part of the helmet manufacturer.
I've noticed a difference in build quality as well depending on price as some helmets feel more "plasticy" or feel looser than others. My $100 helmet that I have now definitely feels kind of frumpy compared to other helmets that I've looked at recently like Schuberth, Nolan, HJC, etc. The new version of the helmet that I own now, which is still carrying a $100 price tag, feels night and day different/more solid than my old discontinued model. The new one feels every bit as solid as the more expensive ones that I've played around with.
The other argument that is out there is by what level did the helmet pass the testing? They all have to pass, but did the more expensive helmet pass the test better than the cheap one? I don't know, I can't find any data to back that up to support or deny that claim. It's like someone else said, some helmets are made for professional use and I'm sure there is a difference in their build quality. But for basic street use, I have yet to really find anything that backs up an expensive helmet being better than a cheaper more affordable one.
Like jackets, boots, gloves, and the bike itself, you buy as much as you can for the budget you have to work with