The weather is getting nicer and Chicago will be filled with (even more) bicycles soon. If you're looking to purchase an old-school Schwinn or similar affordable ride, you might check out this post on Craigslist. If you can't make it, don't forget the good work that the volunteers of Working Bikes do as well, and they also sell vintage cycles. Don't want a used bike? This site has all of the bikeshops in Chicago, and feedback on what people think of the service.