It's trickier than you think! Even for the modern era, the railroad tycoon games are surprisingly deep and sophisticated economic simulations. I still haven't found one to equal Railroad Tycoon 3, which has this kind of neat reactive diffusion field pricing engine.

The modern equivalents (I'm thinking of Transport Fever 2) while they are fun games just lacks the ability to build and manipulate a real economy by doing things like e.g. putting an industry in a town and then transporting goods there to satisfy the industry, making both your train line and the industry wildly profitable.