Once rated for DOT use (legally) any helmet is going to protect your head. The extra dollars are for: graphics, quality of secondary materials, comfort, and aerodynamics.
I have a number of helmets ranging from free (AFX sent to me from revzilla by accident
) to SS1000 (150 ish?) And I had a Shoei back in the day (still saving up for an X12 BB). The main difference IS confort and windnoise, as well as parts that can be replaced and fitted.
I would stick to the normal quality offerings from reputable sources like Bell, HJC, Suomy, Arai, Shoei, Speed&Strength, Scorpion, Fullmer, AGV...blah blah blah. You can shop anywhere from the sub $100 to the $800+ range with those brands. I think someone mentioned closeouts...do it. Buy two or three so you can rotate them. That's what I do so they all last a little longer since I use them every single day.
Anything not legit from ebay or the local flea market isn't worth it.