Target offers the Mane 'n Tail Original Shampoo 32-oz. Bottle for $2.99. Check the Subscribe box and add it to your cart to bag free shipping. (With orders of $25 of more, Amazon charges the same, with free shipping for Prime members.) That's about $2 less than you'd pay in other local stores, excluding the below mention.

Be sure to cancel your subscription once your order ships to avoid being billed for subsequent shipments. Prefer to shop in-store? Walgreens also has it for $2.99 for in-store purchase only. (The link is for reference only. You must visit your local store to complete your purchase.)