Amazon has a 2-pack of Amazon Essentials Women's Classic-Fit 100% Cotton Sleeveless Tank Tops (https://www.amazon.com/dp/B08NX11ZZ8?tag=quackdeals-20) for just $5.90 (originally $19, free shipping with Prime or on $35+ orders). These versatile tanks come in a variety of colors (black, white, tie-dye, etc.) and are perfect for layering or wearing on their own.
(https://m.media-amazon.com/images/I/51X1xR6gCpS._AC_SY879_.jpg)