Keeping an eye out for, dealing, modifying and then field testing non hi-tech "good ole" hunting pants is one of life's little pleasures! I have several pairs for different circumstances.
Here is how I came upon my favorite pair of fantastic, extreme cold weather pants (cost me very little) :
1) I bought two pairs of identical big bellied short legged wool pants from an old army surplus/second hand shop (he was happy to get rid of them)
2) I washed them in hot water and then dried them in a dryer, while examining and trying them on occasionally
3) I ended up with 2 pairs of washable, thick, virtually wind proof pants that fit my waist comfortably but that were much, much too short.
4) I cut about 12" off the legs of one pair and sewed them to the other pair.
5) I used more of the remaining pant legs to make cargo pockets
6) I have lots of spare material for doubling knees if necessary and other modifications as well as future patches.