I have almost the same bike in red an 1980 or so model. I still use it as my back up bike and rides very well. I upgraded some components over the years. Anyway I would replace the bottom bracket and cranks as suggested and basically restore whatever parts from what you can find from that general era. All sorts of stuff comes up on ebay from that time that might fit the frame: wheels, cranks, dererailers,brakes etc. seems to show up at reasonable prices. It is the whole bikes in nice condition that are over priced. What ever you can't find you can look in the box and put back that was origionally on the bike.