I'm cheap. I once rode in 35 degree weather. I had a long sleeve base layer from Target. On top of that I wore another light shirt (almost like a base layer) over it and then my jersey. On top of that I had a windbreaker, and I was fine. I actually ended up taking off the wind breaker halfway through the ride.

I also recommend ear muffs or some kind of cap. Gloves are necessary (for me) at that temperature.