Rewards: 82 Gold, R$82,000
Location: SEASON 1
Unlocks from: Own the Bugatti Bolide
Maximum Required PR: 112.9

This one-horse series is 55 events (53 Trophy + 2 TT) and the gold progress rewards fall as follows:
25%  10GC     needs PR 100.9
50%  16GC     needs PR 104.9
75%  22GC     needs PR 107.7 [which is less than 'all 3s'...more like 1313333 I think?]
100% 34GC    needs PR 112.9 [which is 5343343]

(FWIW I started with PR112.9 and, after the first tier exhausted service life, have so far reached 75% without servicing - very useful when this car has a service lifespan like an adult mayfly! )