Forget all the massively expensive cold-weather layers, this USMC issue Polartec Power Dry Classic 100 half-zip fleece pullover is the best #2 warmth layer you can buy. Usually between $50 and $40 on eBay.
Paired as a number #2 layer with a decent base and solid #3 and shell, this kept me toasty snowshoeing and backpacking in -20 (F) and blowing snow at 12,000+ft in the winter Sierras a dozen miles south of the USMC's Mountain Warfare Training Center.
Works well by itself at lower altitudes and warmer (30 degree) temps. Durable, takes a beating and keeps on heating.