Amazon offers Prime members the Under Armour Toddler Boys' Big Logo T-Shirt in five colors (Midnight Navy pictured) for $6.99 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $5.48.) That's the lowest total price we could find by $11. It's available in sizes 2T to 4T, although not in all size/color combinations.
Note this item has an estimate ship time of one to two months.