I bought a Bell Phi at Sierra Design, online for $35. It was a discontinued model from 2005. It has the better adjustment system found on the pricier helmets. I've always used Bell helmets, so I knew the size.
The only caveat is that I did not think about my mirror mounting. There is very little space to mount the mirror. I probably would have made the same mistake at the LBS though.
Bell doesn't care where you buy your helmet and will replace the pads for free if they are still being made.
If you know your size, then go for it.