Op should probably add that to make billions in 2 days you would likely have to log into Solo and mode switch whilst forgeting about eating sleeping or any contact to the outside world for 48 hours. Even then it would be unlikely.
I've spent 2 hours over the past 2 days, made around 40 million with a 6 tonne capacity corrosive cargo rack, been doing regular mission haulage in between the Palin missions.
Payouts range from 5 mill up to 19 to collect thargoid samples, fortunately other missions also pay well out here, so plenty of opportunity's to vary your activities..
How anyone can mode switch and burn themselves out just to get billions is beyond me.
http://i66.tinypic.com/28jbed5.jpg
http://i68.tinypic.com/145r1i.jpg