Hanes offers its Hanes Men's FreshIQ X-Temp Pique Polo in several colors (White pictured) for $7.50 with free shipping. Outside of the mention below, that's the lowest price we could find by a buck, although we saw it bundled with a pair of boxer briefs for a buck less in November. It's available in select sizes from S to 6XL.

Update: The price has increased at Hanes; however, Walmart still offers it in Blue Horizon for $7 with in-store pickup.