If you're in a thrifty mode, your best bet is this Madewell Open Cardigan. It's a great piece, while not very pricey. Another strong contender for your wardrobe is this Rip Curl Open Cardigan. While the price of this product is not too high, it will surely attract a lot of attention. You might also want to consider this Sejour Open Cardigan. The price is very reasonable, but the effect on your wardrobe will be pretty fantastic.