http://sportbiketrackgear2.homestead.com/EXO-1000.html
Scorpion EXO 1000. It is the only helmet on the market that has a drop-down sun visor and meets SNELL standards (although SNELL 2005, not current SNELL). They cost in the neighborhood of $300, however the Apollo graphic is on closeout for $199.
Your only other option is the Shark S900 which is both DOT and ECE certified. However, it is out of your price range. You won’t find much in the way of reviews on it as it is brand new to the market. However, Shark is known for high quality and high safety.
http://stores.sportbiketrackgear.com/Categories.bok?category=SHARK+Helmets%3AS900
Unfortunately, as ranette pointed out, sun visors are featured mostly limited to modular helmets, which, due to their basic design, can not possibly meet SNELL standards as they are technically considered half helmets since the chin bar is not fixed, and half helmets can not be SNELL certified. The only other Full Face helmets I know of that have a sun visor are the HJC IS-16 and HJC FS-10 which are pretty bottom-of-the-barrel compared to the other two I just linked and not even worth comparing to them. They are DOT certified only.