Wool...You can get pants for under a hundred and a good jack shirt (wool also) for around $60. Smart wool longjohns and you can layer more shirts so it can be removed as it gets warmer during the day. Cotton kills thats a fact so don't even think about it.
Several companies make wool pants:
Woolrich
Johnsons (vermont)
Bid wool overalls are nice but they get real warm.