Agree with others. Maybe if you compare what your car can/cluld do at the end of the day compared to, say, a 40k car, a 65k car, maybe even higher in some cases, then the logical amount is whatever makes your car perfrm as good as/better than that, but for less.
24k car+10k mods, but performs better than 50k car = logical
24k car plus 5000 in stance and visual mods that you enjoy turning heads with? Up to you, i guess logical. At least the car is a sranceable car in the scene
24k car plus 30k in mods? Youve surpassed the cars own value in mods. But if thafs what you wanna do fuckin do it!