Bike specific clothing is nice for bike commuting but not necessary. In cold weather the layering technique works with any winter clothing. If you want to purchase an item of bike specific clothing, I think the most essential one would be rain gear- specifically a jacket. I have a "showers pass" jacket that was expensive but you can find cheaper ones. I have purchased the plastic rain jackets from Performance but they rip so you may want better quality. I would think for $30 to $50 you could find a servicable jacket. Make sure it's waterproof and not resistant and you'll want some venting. You may also want rain pants and shoe covers. For your head, wear a ball cap under your helmet. You are now good to go.