The variable cost of running a train is based on maintenance costs, crew cost and fuel cost. This is not that hard to compute because we know how far each train runs, what each crew was paid and what type of locomotive was used. The weight of the cargo is not available so that is not part of the variable cost.

The yard fee would be by car and terminal fee would be by passenger or express train for each session (because we are having fun and want to be fair fees would be the same for everyone). There are many types of terminals. You can have icing, marine, stock yards etc.. The Rock County has several passenger and express terminals, one large marine terminal and a perhaps small icing terminal at a later date. My stock yards will be company owned so it will not have fees but in many cases this would not be true (in our world the owner of the livestock pays by head count in the cases I know about). In the case of Rock County any cars that need to be weighed are weighed by the company crew on a company scale as the other cars are weighed off the layout.

So we end up with variable cost that seem manageable. There is maintenance and fuel costs that are computed by the computer for each session based on the equipment used and how many miles or hours you run them. The crew cost is by contract between the manager(s) and the crews for each train they run.