For Amazon Mom members, Amazon offers the Johnson's Baby Shampoo 15-oz. Bottle 2-Pack for $3.22. (Amazon Mom membership is free; click here to sign up.) Order via Subscribe & Save and it drops to $2.65 with free shipping. That's $1.33 per bottle, the lowest total price we could find by $11.
Be sure to cancel Subscribe & Save once your order ships to avoid being billed for subsequent shipments.