What do I really need for cold weather cycling?

Last week I was only able to ride my bike for one day. The other days were taken up by an all day conference I was required to attend. It was held in a hotel, and short of taking out a room ($$$), there was no way for me to bike, shower, and hang wet clothes for the day, so I reluctantly gave up and rode the subway. The weather this weekend was also bad (thanks, Irene!), so I haven't gotten much exercise, and I can definitely feel the change in my mood, and the increasing tension in my shoulders. I really *need* to ride my bicycle!

September is also rolling around, so I've been thinking a lot about how to keep up my bicycle habit during the colder season. Both the temperature drop and the decreasing daylight will be a challenge. As a good salesman, the owner/manager of one of the bicycle shops I frequent has started talking to me about acquiring a winter cycling wardrobe. This bicycle shop sells safety helmets for $250, so I have a feeling that, whatever I get, I won't be buying it there. (My current helmet -- same brand -- cost me about $35, and I don't really think theirs is almost 10 times better. )

That said, all clothing that is cycling-specific seems to be very expensive, no matter where I look. I know I need protection from wind, rain, and cooler temperatures, but do I really *need* cycling-specific clothing to ride 20 miles a day through the winter? If you have a limited budget, as I do, what are the must-haves I should spend my limited funds on, and what are the nice-to-haves that I could, perhaps, put on my Christmas list?

Do you have any thoughts?