If you are on a tight budget, your best bet is this Zella Tank. It's a popular product, while not very pricey. Another strong contender for your wardrobe is this Yummie by Heather Thomson Tank. While the price of this piece is not very high, it will certainly attract a lot of attention. You might also want to consider this Ivy Park Tank. The price is very reasonable, but the effect on your wardrobe will be pretty fantastic.
If you're looking for something in between pricewise, look no further than this Ella Moss Tank. This item won't break the bank, but definitely deserves a place in your wardrobe. In this price range, you can also take a look at this AG Jeans Tank. It's an attractive option both price and quality-wise. And do check out this Eileen Fisher Tank! It's a very popular item and good value for money.