I have a pair of Ray Ban aviators fitted with Essilor's poly lens and the Crizal Avance AS/AR treatment. The lens stock ran about $100 by itself. The coating was free with a voucher, but runs another $100, usually. The frames go for around $20 if you know where to look.
First off, the lens actually has an ANSI rating. They double as outdoor shooting glasses and actually provide that level of protection. They're not acid-proof lab goggles, but you won't find better protection in that design. The AS/AR treatment is not a coating, but a bonding agent that is baked into the material. This produces an unusually hard surface that is impervious to accidental damage. The polarizing and AR create exceptionally low distortion (read a flying magazine for a rundown on that one), and prevent the slightest bit of glare. They weigh almost nothing (less than half the weight of the original Ray Ban lenses), and work like a charm.
Featherweight, non-refractive, no-glare safety glasses that dim the sun. They're Aviators, which means that they're supremely badass looking to boot.
Walmart specials don't compare. They typically have no AS/AR coating, they are usually not polarized and many have measurable refraction. The UV "protection" is sometimes damaging to the eye. Much of the $5-15 stuff has a substandard UV coating that allows penetration into your dilated eye. Now, take a hammer to the material, and then tell me what you want in front of your eyeball at the range.
Higher-end lenses are usually polycarbonate. It scratches easily, but is shatterproof. Add in a good AS coating, and they're indestructible. There are other plastics, but they're typically used in prescription lenses because of their refractive qualities. Some manufacturers still use real glass, but I have no idea why.
Oakleys are a whole 'nother ballgame. Any lab can make a good set of lenses for almost any common frame, but nobody but Oakley makes their lens. Even prescription lenses have to come from the manufacturer.
As for The Girl's $600 Fendi sunglasses, I got no clue. They're the same lenses as mine, but they retail for more than my first car.
