Edit: fixed teh prices...
At this point, there is no reason not to get an SA2005 helmet. They are designed for use in cars which includes side impcats, and fire resistance. Open and full face start at about $150. Careful not to select the m2005s that show up.
Full Face:
http://froogle.google.com/froogle?bt...line&scoring=p
Open:
http://froogle.google.com/froogle?bt...line&scoring=p
Weight is the biggest issue. Buy the Lightest SA2005 in teh style you want that you can afford within your budget.
One of the past issue SportsCars has a chart I think that has weights.