For $40 you can have what I use for coyote hunting in negative 20F. I'm 6'2" and 180 lbs. The medium longs fit about right (a little loose in the waist).
Military issue Primaloft insulated trouser pant is part of the Extreme Cold Weather system and meant to be used as an over-pant in inclement cold weather.
I use the ecws level 7 in Wisconsin in January and have no complaints. Packs down small enough and super warm. You do not want to be moving in them as you will get sweated up quickly.