Rewards: 56 Gold, R$56,000
Location: SEASON 1
Unlocks from: Own Any Car in the Series
Maximum Required PR: 58.3

There are 51 events - 48 Trophy + 3 TT – with each car having a specific TT and 2-event showcase, and only the Blackwing can be upgraded enough to open the last 3 cup races (PR53.8/56.1/58.3).

Progress Rewards split:
25% - 7GC and R$7,000      [PR 38.9 using Hellcat, PR 42.0 otherwise]
50% - 11GC and R$11,000   [PR 44.0 using Hellcat or Stingray, PR46.5 for Blackwing]
75% - 15GC and R$15,000   [PR 48.6]
100% - 23GC and R$23,000  

As you can see, any one of the cars can reach 75% on its own 

Upgrade costs for the Blackwing will be:

(As usual, courtesy of Paulo over on FB RR3 Trackside)