Tiger Outfitters via Amazon offers the Blackhawk Men's Memory T-Shirt in Black or Grey for $4.99 with free shipping. That's the lowest total price we could find by $15. It's available in sizes S to 3XL, although not in all size/color combinations.
HisRoom cuts up to 70% off a selection of men's and boys' clearance items, with prices starting from $2.99. (Prices are as marked.) Shipping adds $5, or get free shipping on orders of $40 or more. Some sizes and stock are limited. A couple of best bets:
Walmart offers the Fruit of the Loom Men's Short-Sleeve Pocket T-Shirt in 13 colors (Black pictured) for $3.58. Choose in-store pickup to dodge the $4.97 shipping fee. That's the lowest price we could find by $2. It comes in sizes S to XL, although not in all size/color combinations.