2.99 for a Nokia bluetooth headset + free shipping.

http://www.buy.com/prod/nokia-bh-102-wireless-earset-wireless-connectivity-mono-over-the-ear/q/loc/101/209307668.html?adid=17070&dcaid=17070

Does it work under a helmet?

That is a steal of a deal.

Does it work under a helmet?

there's a thread on kawiforums where a member took a laptop speaker and wired it to the headset inside his helmet.
i'll look for some small laptop speakers this weekend and see if i can create something similar.