After you win the first three races. It keeps on opening up three tiers. One for Audi, NextEV and one for Renault.

To get the first five sponsorships is easy enough with the race PR 50 needed in the Renault Hong Kong challenge. 

Then the last two tiers PR shifts to 52 and probably more. To acheive that PR at least the 120 GC engine upgrade needed and probably two more cash upgrades. 

So if done for all three cars its an outlay of 360 GC or more, besides whatever already spent to win car. 

Basically the 300 GC can be seen as a discount on upgrade, nothing more. Not the free giveaway, as advertised as an incentive to finish the sponsorship series.

They should have kept the PR the same as required to finish the Hong Kong E.Prix.