If you're budget-restricted, this Asos Tank will fit the bill. It's a popular choice, while not very costly. In this price range, you can also consider this Asos Tank. It's also a popular item and won't break the bank.
If you're looking for an item in the middle of the price range, opt for this Asos Crew-Neck Tee. While the price is very reasonable, this piece is an easy wardrobe update. It's also worth looking at this Asos Crew-neck T-shirt. This piece is ultra popular and, just as importantly, not very expensive.