Ninja Inga mentioned most of the stuff.
Blue B/S British Standard is for motorbike stuff like his AGV helmet.
Red B/S British Standard is for Car Racing which comes with nomex lining.
SFi is another lesser known standard that the americans normally use but not many ppl use this standard these days
Snell SA2000 is actually in Gold. But if u're gonna get this helmet might aswell wait for SA2005 to come out.
Snell helmets are generally more expensive somehow. Lowest asking price is 1500.
I've an Arai GP5K that cost me 2600.
But the number 1 question is do u want a helmet with an intercom or not? If u can pm me your contacts i know someone who wants to sell his Sparco with intercom helmet 2nd hand.
Another link u can check out.
http://morris-racing.com/kartingmalaysia/classifieds.php
There is some helmets for sale.