Aaah. Ashtabula cranks. http://www.sheldonbrown.com/opc.html

It's probably not worth buying all the parts needed to build it up. You can try Bike Kitchen, Pedal Revolution, or that shop on 14th at Guerrero (if it's still there) for old cheap parts. It still may cost a bit once you get all the parts together. Check Craigslist for older complete bikes to strip down and rebuild.