I have a Giro Atmos, a Specialized, and a Louis Garneau TT helmet. A few weeks ago I saw a no name road helmet and a Zefal mountain bike (visor) helmet in the "sales" bin at WalMart for $9 and $11 respectively. Both were certified. They both fit so I bought them.
The no name has as many vents as the Atmos, and is lighter, but has no carbon fiber. I like it better than any helmet I own. Who would have thought it?