Checkout this thread do get your stolen digital $'s back.
https://www.gtplanet.net/forum/threads/comprehensive-money-earning-guide.387680/
Some examples of the bigger earners:
Race 8: Nostalgic 1979 Series - Circuit de la Sarthe (Chicaneless)
Difficulty: Easy
Car: Ferrari 330 P4, Jaguar XJ13, Ford Mark IV, Shelby Cobra Daytona or Aston Martin DB3S
Reward: 240k per Clean Race
Time: under 7-8 minutes
This is the option two. Roughly the same as Monza in terms of strategy: 330/Xj13/Mark 4 can win stock (but should be upgraded to cut down lap times), Daytona and DB3S with upgrades, not sure about 250 GTO, Alfa and Gordini are useless
Race 9: La Festa Cavallino - Willow Springs Circuit (Big Willow)
Difficulty: Easy-Medium
Car: Ferrari Dino at N200
Reward: 342k per Clean Race
Time: under 11 minutes
This race can be won relatively easy with a specifically tuned Ferrari Dino: put the power at N200 max, reduce the weight to minimum, Sports Soft tyres, set up the custom gearbox so the car maxes out at roughly 250 km/h and make the suspension a bit stiffer. You can adjust the differential as well if you feel like the car is too oversteery for you, but i personally kept the diff stock, the car is manageable enough to be driven comfortably at high speeds.