If you're looking for a good deal, take a look at this Nobrand Crew-Neck Pullover. While the price is very reasonable, this item is an easy wardrobe update. In this price range, you can also look at this Marc Jacobs Cardigan. It's an attractive option both price and quality-wise. Alternatively, opting for this Cardigan is a nice choice as well!
If you're looking at it like an investment piece, then you absolutely must check out this Rag and Bone Crew-neck Sweater. This piece seems expensive, but it's worth it. While you're at it, also have a look at this MS MIN Open Cardigan. Yes, this item is expensive, but it does not mean it's not worth it.