Amazon offers Prime members the Assassin's Creed: The Americas Collection for Playstation 3 for $19.99 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping adds $4.98.) That's the lowest total price we could find by $18.
Don't mind collecting it? GameStop also has it via in-store pickup for the same price. (Shipping adds $3.50.)