Another source is
www.saferacer.com where I got my Bell a bit cheaper because of shipping policy vs. helmetcity's.
I test fitted the Bell at the SEMA show and agree that different head shapes may work better with different helmet brands. Vents don't help us much as we (most of us) aren't on motorcycles. High priced helmets are often because more advanced materials are used to save weight. We don't use them for very long so that is les important than for motorcycle riders. OTOH if you go to the Snell website, you will see that the SA series have several advantages for us vs. the M series.
http://www.smf.org/
http://www.smf.org/standards/pdf/sakartfinal1204.pdf