if you're in a thrifty mood, why not take a look at this Enza Costa Rollneck. It's a popular item for a reasonable price. Another strong contender for your wardrobe is this J Brand Turtleneck. While the price of this piece is competitive, it will definitely attract a lot of attention.
If you're looking for a happy medium, consider this Nili Lotan Turtleneck. While the price is very reasonable, this piece is an easy wardrobe update.