Amazon offers the Nizoral Anti-Dandruff Shampoo 7-oz. Bottle for $13.60. Add it your cart via Subscribe and Save, and the price drops to $9.52. With free shipping, that's the lowest total price we could find by $13. It features the active ingredient ketoconazole and is meant to be used twice a week.
Be sure to cancel Subscribe & Save once your order ships to avoid being billed for subsequent shipments.