Where did Lucas get the money to finish Star Wars?

An interesting facet of the production of Star Wars (1977) is that it was very heavily edited; in fact, it even won an Academy award for editing. A lot of the original raw film was terrible, and the original script and scene sequencing was deeply problematic. The deep editing process corrected a large number of serious flaws in the original footage and script. This was often accomplished with voice overs and sophisticated inserts. For example, in the original form of the production it was not clear what the alliance characters were doing by infiltrating the Death Star. This was fixed by adding an insert showing Obi Wan Kenobi disabling the tractor beam. This insert features an elaborate set and animated graphics.

Obviously, this extensive post-production editing process and addition of many inserts with their own sets must have been very expensive. I wonder how it is that this money was found. I understand that originally Lucas was on a shoestring budget and that personally he was broke. His car got repossessed and he was rationed to eating one stale Big Mac a day. How is it that such a penurious production was able to find a large sum of money to do the elaborate editing and post-production work that greatly improved the final result?