I think $500 on a helmet is pretty normal. A lot of helmets cost that much. You are paying partly for crash protection and engineering, but also for a light weight fiberglass shell instead of plastic, smooth finishes that are comfortable to use, good aerodynamics and padding that reduce noise, good optics from the visor, and features. Around $500 seems to be a sweet spot in the market where you can find a lot of safety combined with a lot of comfort and quality. I ride with a plain white lid that has a high protection rating and cost $500. Jazzed it up a little with some fancy strips of orange tape (now I look like Rossi!). Works great. Very comfy.
The Marushins and other brands from the article posted by Wintrsol do seem to offer high levels of protection for a lot less money, though. Funny those weren't on display at Cycle Gear on helmet shopping day.
Also funny that the helmet most favored by the BMW crowd, the Schuberth R1, was rated among the worst by the SHARP program. (I only laugh at BMW people because I like them.) (Okay that's not the only reason.)
I think another oft forgotten safety feature is helmet color. On the road, especially in gray conditions, a white lid stands out. So does hi-viz yellow-green, if you can bear to wear that. Black helmets are harder to see in traffic.