Walmart offers the Fruit of the Loom Men's Classic Thermal Underwear Bottom 2-Pack in several colors (Grey/Natural pictured) for $11. Opt for in-store pickup to dodge the $5.99 shipping fee. That's tied with last week's mention and the lowest price we could find by $9. They're available in select sizes from S to XL.
None of these moves requires a big investment, and they all can save you money.