If you are on a budget, your best bet is this Nike Round-neck Sweater. It's a popular piece, while not very pricey. Another strong contender for your wardrobe is this Nike Jumper. While the price of this piece is not too high, it will surely attract a lot of attention.
If you're looking for a happy medium, why not opt for this Nike Jumper. While the price is very reasonable, this piece is an easy wardrobe update. Why not also look at this Nike Crew-neck Sweater. It's an attractive option both price and quality-wise.