If anyone can do Zenith Series, try Silverstone Grand Prix in Mastare Global Championships Grand Finale (near the end of this series). With  100% daily bonus, it  gives $51,900 plus massive friends bonus.

The event is pretty easy I guess (due to short cuts) you're guaranty o get 1st place. I'm using Agera R, cost about 5k for service and take up to 5 hours. I don't care, I do that before go to work anyway....

The problem is I have only a few friends doing it everyday 

if you can do this series, please add me in GC: Buffman. 

With 20 friends doing it everyday, I believe the daily bonus can be in 100k+ easily.