If you're not planning on spending much, your best bet is this Bandana. It's a wonderful piece, while not very costly. In this price range, you can also consider this Beret. It's also a popular item and won't break the bank.
If you're a bargain shopper, we've got your back with this Hat. This item is likely to become a total wardrobe staple. Another great option is this White + Warren Beanie. It's an attractive option both price and quality-wise. Look at this SAM. Beanie too! Great value for your money.
If you can afford to splurge, then you absolutely must check out this Eugenia Kim Hat. This piece seems pricey, but it's top quality.