Rewards: 71 Gold, R$71,000
Location: SEASON 1
Unlocks from: Own Any Car in the Series
Maximum Required PR: 66.2

There are 51 events - 48 Trophy + 3 TT – with each car having a specific TT and 2-event showcase, and only the Camaro will be able to be upgraded enough to open the last 2 cup races (PR 65.3/66.2).

Progress Rewards split:
25% - 9GC and R$9,000       [PR 47.0 using Blackwing, PR 51.4 otherwise]
50% - 14GC and R$14,000   [PR 54.5 using Blackwing or Shelby, PR 58.8 for Camaro]
75% - 19GC and R$19,000   [PR 61.7]
100% - 29GC and R$29,000  

On its own a fully-upped Blackwing can only manage 64%, a fully-upped Shelby 84%, both together 90%.

Upgrade costs for the Camaro are still unknown AFAIK...
#EDIT July 10 #  Courtesy of Paulo over on FB RR3 Trackside we now have the upgrade costs: