Rewards: 60 Gold, R$60,000
Location: SEASON 1
Unlocks from: Own Any Car in the Series
Maximum Required PR: 66.0

There are 51 events - 48 Trophy + 3 TT – with each car having a specific TT and 2-event showcase, and only the Corvette can be upgraded enough to open the last 3 cup races (PR65.2/65.6/66.0).

Progress Rewards split:
25% - 7GC and R$7,000      [PR 48.7 using Viper, PR 52.1 otherwise]
50% - 12GC and R$12,000   [PR 54.6 using Viper or Shelby, PR60.1 for Corvette]
75% - 16GC and R$16,000   [PR 63.9]
100% - 25GC and R$25,000  

A fully-upped Viper can reach 60+%, a fully upped Shelby 82%, both together 88%.
The Corvette will probably have total gold upgrades cost of 519GC to reach series completion, based on the initial details: