If you're riding in cold weather and on a budget, layers are the way to go. Plenty of other fitness tops, jackets, etc. will work just fine for cycling. A lot of my hiking and skiing stuff gets pressed into service. I do like Owlie does and use unpadded tights with shorts or bibs underneath, so I can ride multiple days without needing multiple pairs of tights.

If you decide that you're into cold weather riding or you're really cold-blooded, a dedicated winter cycling jacket makes sense. It's so much easier to get dressed, and I feel less like the Stay-Puft Marshmallow man. (BTW, I have a nice winter jacket for sale in the "For Sale" forum!) Same thing with winter cycling boots- they just make the whole process easier.