Vitanity Inc via Amazon offers the Bamboo Hair Brush for $11.99. Coupon code "4E2VH23G" cuts it to $7.19. With free shipping for Prime members, that's $5 off list and the lowest price we could find. It has a selection of natural bamboo and wooden ball-tipped bristles.

Update: The price has dropped to $8.99 before coupon, $5.39 after.