Woot offers Amazon Essentials Mens V-Neck Undershirt Breathable Cotton Pack of 6 for $9.99 (reg. $23.90) free shipping with Prime. 

Product Description:
Amazon Essentials' casual undershirt design, offering both comfort and functionality for everyday wear.
 

• SLIM FIT: Slim fit through the shoulders, sleeves, chest, and waist
• GARMENT LENGTH: 29" from side neck on US size Medium
• COTTON JERSEY: Soft, smooth cotton. This breathable lightweight natural fabric feels soft against your skin, while the added spandex offers a flexible fit that moves with you
• V-NECK UNDERSHIRT: A casual undershirt design, offering both comfort and functionality for everyday wear
• DETAILS: Designed with short-sleeves and a straight hem which are finished with super soft flexible stitching. The v-neck is banded for extra durability and has a printed label at the back neck
• Certified STANDARD 100 by OEKO-TEX, which requires textiles-based products to be tested against a list of 1,000+ chemicals, to limit those which may be harmful to human health
• 100% Cotton