Early on the progression rate seems okay. I'm probably at around 4 hours in.
I've purchased:
-911 GT3 (997) '09 - 142,400
-Fairlady Z (Z34) '08 - 39,100
-Mini-Cooper 'S" '65 Upgrades:
-Sports Computer - 1,600
-Sports Air Filter - 700
-Sports Muffler - 1,500
-Sports Brake Pads - 400
-Street Suspension - 2,500
-Weight Reduction: Stage 1 - 3,500
-Sports: Medium - 2,800
-Bore Up - 5,000
-High Lift Cam Shaft - 5,000
-High Compression Pistons -
-GTO Twin Turbo Upgrades
-Sports Computer: 1,600
Car Wash - 50
Total Credits On Hand: 1,791,350
Pre Order Bonus: 100,000
Digital Deluxe Bonus: 1,500,000
I honestly didn't notice this on either car I purchased.