If you are looking for tanks like c & c, Rebecca Beeson makes some and you can get them at Urban Outfitters for about $24. I actually like them better than c & c because they have a rolled edge at the bottom, which makes them smoother and easier to layer with. HTH!
my two cents re the old navy ones: i have two and i don't like them nearly as much as my c&c ones in the same style. they're shorter in length (barely come to the top of my pants) which is a big issue for me, and the sleeves aren't nearly as long. goclothing has lots of c&c stuff on sale for around $30 and there's a code on reesycakes for an extra 15% off. eluxury, shopbop, rafael hawaii, and active endeavors also have tons of c&c on sale. any you can get them at some discounters (nordstrom rack comes to mind).