Just floating another idea, imo one of the most direct and simple ways to reduce player profit (assuming you need to as i said earlier its difficult to say) is to increase taxes.
Currently they arent active, but when they are (next version i think) they could always be increased to be more of a burden on the player.
At the moment i think they vary from about 15-35%.
Another simple idea would be to increase the amount of money it takes to upkeep factories. (Branches are already fairly expensive, you cant make large ones unless you sell well into the thousands) This would directly impact on profitability of your cars per unit.
Edit: I found the thread where i was talking about design costs and exponential increases in cost here.
Currently they arent active, but when they are (next version i think) they could always be increased to be more of a burden on the player.
At the moment i think they vary from about 15-35%.
Another simple idea would be to increase the amount of money it takes to upkeep factories. (Branches are already fairly expensive, you cant make large ones unless you sell well into the thousands) This would directly impact on profitability of your cars per unit.
Edit: I found the thread where i was talking about design costs and exponential increases in cost here.