Regarding price vs. protection. Back in the late 60's I think it was the Snell Foundation that did a study on helmets and motorcycle accidents. Accident reports, photos and autopsies on thousands of fatal motorcycle accidents over a long period of time. It was about 100 pages and one of the cycle mags of the day ran a series of excerpts from it.
I think the study was done to establish the first set of helmet standards, and for a while a Snell certificate meant you had a pretty good helmet. Don't know if Snell is still involved in certifying helmets.
Anyway, as I recall, one of the findings was that virtually any helmet was better than nothing(DUH), but that once you got beyond a very low level of price there was little if any difference in protection from impact. The only difference seemed to be that the more expensive fiberglass helmets were more resistant to penetration(that is, from banging your head into a pointed object). They were also more resistant to weakening due to ultraviolet radiation, paint and cleaning solvents.
Bottom line, any approved helmet will provide approximately the same amount of protection from impact, paying more buys comfort, style, and brand prestige, but little additional protection.
