I got an AFX helmet on Ebay from Dennis Kirk's closeout store (DK-trader -
http://stores.ebay.com/DK-Trader )... brand new, for like $20, shipped! They may be display models, closeouts, small scratches, etc, but I didn't care about that! Mine had a couple light scuffs on top where it had been taken in and out of the box a few times, but I was ok with that.
I buy from their website too, DennisKirk.com, and have always received the best service and great stuff. Highly recommend them.
Also, I have done quite a bit of research on helmets and agree with Daeldren... the more expensive ones may be a little more comfortable, maybe more cool looking, etc, but protection doesn't increase nearly as drastically as the price does, if at all. Some very inexpensive helmets have been proven to provide equal or better protection.