I have commuted my 12mile round trip for the last 5 years and never bought a single item of bike-specific clothing except a helmet. Winter clothes are a scarf to cover the face and neck, a couple of layers of long sleeve t-shirts, fleece, waterproofs if wet. lightweight cotton pants under sweat pants and 2 pairs of socks with a carrier bag between them for waterproofing. Make sure your shoes are tied loose otherwise you'll make your feet cold cos the bloodflow is restricted.
That's for a really cold day. The hardest part is getting the balance right between warmth when you start and sweating buckets after 1 mile.