I'm going through the same exercise myself - if I buy a pair of tights I'll need a paper bag to wear over my head at the same time and i could scare more than a few motorists........

Under Armour has cold gear tights that run around $50 a pair (still a little rich for my budget) - I'm leaning towards wind resistant track pants (available pretty cheap if you hit the outlet stores) myself and when it gets even colder a pair of wicking long johns underneath.