Good news! You probably already own everything you'll need. Old wool sweaters are perfect for cool rides. As it gets colder, add another layer. Layer everything. I sometimes wear 3 pairs of gloves, 3 tops, 2 pairs of socks. I usually get by with just knickers on the bottom, but if it's much below freezing, I'll wear a pair of tights over them. Nothing really needs to be cycling specific. You can get really cheap arm and leg warmers in places like Target or Old Navy. Oh, and most important, cover your face and neck. I use a Buff for that.