Nayked Apparel via eBay offers the Bella + Canvas Women's Racerback Tank Top in a copious amount of colors (Athletic Heather/Pink pictured) for $9.08 with free shipping. That's $3 off list and the best price we could find, outside of the mention below. It's available in select sizes XS to XL.

Various sellers via Amazon have it for as low as $7, although prices varies by size and color.