I think military surplus Gen 3, Level 2 base layers are the best combo of price, comfort, warmth, weight, breathability, and bulk. They are made of the same Polartec fabric that Patagonia uses in their R1 series which goes for around $100.
Personally I like to wear Smartwool or other brand merino wool simply for the no-stank factor. But the surplus stuff is better in almost every other category.