If you can’t spend much, your best bet is this Obey Crew-Neck Tee. It's a fantastic piece, while not very expensive. Another strong contender for your wardrobe is this Dickies Crew-Neck Tee. While the price of this item is rather reasonable, it will definitely attract a lot of attention. You might also want to consider this Uniqlo Crew-neck T-shirt. The price is very reasonable, but the effect on your wardrobe will be pretty fantastic.
If you're after a bargain, look no further than this Cycle Crew-Neck Tee. This item doesn't cost a fortune, but absolutely essential in your wardrobe. In this price range, you can also look at this Fanmail Crew-Neck Tee. It's an attractive option both price and quality-wise.