PyrotectHelmet
 

There's been the occasional thread on affordable helmets. I wanted to add an option - I went to Bell Motorsports looking for an M2, but ended up with a "Pyrotect" full face helmet that looks exactly like a Bell Sport III but is SA2000 certified. $268. I don't know if Bell is trying to make Pyrotect a lower-end brand or what, but seems worth a look for an inexpensive helmet.

Edit: Sorry, corrected myself - it looks like a Sport III.