Kind of an irrelevant question I suppose - but did they have to pay for the fuel at each stop? The way it's written the various bases gave them fuel and other things out of kindness.
A banker in Australia advanced them $500 USD, which was enough to finance the rest of the journey.
I believe that would be about $9k USD adjusting for inflation, which feels oddly low given the length of the flight, but I suppose they wouldn't have needed to pay for fuel or supplies at PanAm stations.