Helmets are built using various head-shaped moulds, some round, some more oval, etc. The trick is, by trial and error at your LBS, to find what maker uses the mould most like your head is shaped. Once you find that, you tend to stick to that brand--not because it's the best, but because it fits, and fit is critical in helmets. If it won't stay on your head at impact, it's useless.
Price does not reflect the general level of safety. Helmets are usually certified CPSC or Snell or sometimes both. There are some significant flaws in the certification systems, due to impact research and improved technology being able to analyze how cyclists suffer head injuries and exactly what happens (rotational impacts, direct impact, high speed vs slow speed etc.) The old stagnant certifications do not take this into account, but it's the best we have right now. Some helmet makers are beginning to dabble in dual density structures, and rotational systems, but it is not widespread yet.
So, what IS the difference between that $35 helmet and that $225 helmet? They both meet whatever certification the maker has chosen to follow, right? Pick them both up--you'll find the expensive one weighs a LOT less, and generally has a lot more vents (holes). Yet it still passed certification. That is the real difference. It weighs a lot less, and cools your head better yet is strong enough to protect your bean. Higher end helmets also tend to consider style a bit more, and may offer better fit adjustments and other refinements.
Enough background...I am a Giro helmet user. For me, they fit well, and they just proved to me, that they stay on when I need them to, and they break when they are supposed to! Since I broke my helmet Wednesday night, and had a pay-ride yesterday, I obviously needed to get a replacement helmet by then. On pay-rides here in Texas, and probably everywhere else in this country, you are required to wear a helmet during their event.
I went down to my LBS, since they did carry Giro, and I like to spend some money there when I can. It's a good shop, with the right "feel" to it, and they treat me like a real cyclist, not some freak because I ride recumbents. I appreciate that. The Monkeys and I went down to check out their offerings. Immediately, Monkey1 says "Mommy!" There, on the wall, was a helmet...you couldn't miss it from a quarter mile away it was that loud. It was a Giro, even better! Headache (Hi-Viz)Yellow, with reflective striping from Giro already applied! Be still my heart....I popped it on, dialed down the Rok-Loc 5 retention system, and knew my brief search was over. It didn't even cost 3 figures!
The Giro Savant was designed for folks like me--urban road riders who want a lighter helmet, with good venting for those hot summers, and an eye-searing color to add one more level of safety by trying to catch the eye of distracted drivers. This one even has reflective stripes added by Giro to help outline your head for those of us who ride in the dark. I immediately added some red reflective tape to the rear of the helmet to better light me up to drivers approaching from behind at night. My work passes the flashlight test well! The red reflective really "pops" in the dark when you hit it with light.