The best under layers I have found is the silk underwear from the ski catalog covered by merino wool underwear. Up top I wear a wool shirt, a wool sweater, and a fleece vest under my hunting jacket. A wooly-pully cap is very warm. Down here in Georgia, it is very seldom that all this much warmth is required, but since it is layered, it can be adjusted to any changes in temperature.
A lot of guys sweat very easily, which is a problem walking in. Carrying in some of the clothes helps. I once read of a guy who carried a towel into the stand and dried down thoroughly before putting on the needed layers. For outer layers, when rain is not an issue, it is very simple. I either use militay surplus BDU's or Carhartt field pants. Being diabetic, my biggest issue is cold feet so I use more insulation in my boots than most.
Warming layers can often be bought very cheaply at thrift shops, particularly wool sweaters. For most of us, it is not necessary to spend the money that some of the leading brands command, while still being decked out effectively. Maybe the deep wilderness expeditions into bitter winter weather may require the super expensive stuff. However, a morning in the lower 40 wood lot does not need to cost as much as an African safari.