What is themost cost effective way to fix my rear suspension?

The rear on my 70 duster is sagging bad. The leaf springs and shocks are both totally worn out. In the long run I would want to replace it all and return it to a factory state, or close to it, but right now I don't have the money to do it all. What is the most cost effective thing to do right now that will support the rear end better until I can finish it all? New leaf springs? New shocks? Where should I get them from?