check out ebay for older frames with a rigid fork, and braze-ons for fenders and racks. probably what you'll find is mostly steel frames, which would seem to be a poor choice for winter muck, salt and wet, but if you Framesaver the insides, a good steel frame should work just fine as a winter beater, provided you keep it clean and maintained. probably should be able to find something fairly cheap.

buy a set of fenders for it, mount them using the braze-ons, and you're good to go.

something like this

http://cgi.ebay.com/90S-BRIDGESTONE-...QQcmdZViewItem

except that Bridgestones go for a bit of a premium on ebay.

maybe this, buit I can't tell from the pic whether it has braze-ons or not.

http://cgi.ebay.com/Specialized-Hard...QQcmdZViewItem

not so up on other brands, but any Trek 800 or 900 series bike, or any Specialized Hardrock or Rockhopper from the late 80's/early 90's should fit the bill.