The minimum amount of money you will need is 7,000
Cars can only be upgraded in Grid Online.
The cheapest car to get this trophy with is your starting car the Tier One - Alfa Romeo Guilietta Quadrifoglio Verde as it will cost 7,000 and you already start with 5,000.
Whilst in Grid Online head into 'My Vehicles' and select the Alfa, then open 'Upgrades'
The cheapest set of upgrades you want to buy is:
Engine - Tuning Stage One & Two
Drivetrain - Gearbox and Differential
Handling - Weight Reduction Stage One and Suspension.
Once you have bought these you will be notified that your car is entered the next tier and upon accepting the trophy will pop.
DLC CARS DO NOT COUNT FOR THIS AS THEY CANNOT BE UPGRADED