I ride all year round in the state of Maine, down to about 0 F, I don't have any bike specific clothing. I wear long underwear in the colder temps. If you aren't planning to ride below 35 degrees, I would think that you would be okay with almost anything over your shorts. I find that at around 35 degrees I need to wear my 180's earmuffs and my leather insulated gloves (unless it is raining, then i go with my wind/waterproof gloves), my ears get cold and my fingers get cold. Other than that I am okay with regular clothing.

I have found that in the winter after about the first mile or so, I have plenty of heat. YMMV