If the CTA doomsday actually does happen, consider riding a bicycle for at least part of your commute. Chicagoland Bicycle Federation (CBF) has a page of suggestions for some bus route substitutions. If you usually take a bus to a train, you might use a bicycle for that portion, as there are now bike racks in and around many CTA and Metra stations.
For everyday or year-round use, a beater bike might be appropriate. Working Bikes and Uptown Bikes are good sources for used bikes. Police auctions are another source. When buying a used bike from any source, it's worthwhile to take it to a bike mechanic you trust to check it out and make sure that all is in safe operating condition.
The Chicago Bike Shop Directory is a good source for finding dealers and mechanics near you. It includes user reviews.
The Bikewinter web site has lots of useful tips for riding in winter, and if you want to meet folks to ride with, there are plenty of events.