I play with non-PAX cargodist and sometimes speculate how I would like it to work. Some possible thoughts.
(1) receiving stations or industries bid for discrete cargo packets / contracts (whose size can be scaled as a setting). (Once they win packets, their next bid is lowered. Some industries (maybe black hole industries like power plants) may have a higher starting bid). Bids can be dependent on things such as catchment population, so that large cities can receive goods and food etc in proportion to population. Variance can be added to bids, which is high for cargos like goods, food, alcohol etc (as these cargos come in many different forms and there will be cross-map demand) while it is lower for cargos that vary less (coal, oil, grain).
(2) producing stations or industries determine cost of paying transport to each bid, choose the lowest bid, and the cargo is set into that route and destination.
(3) contracts regularly re-negotiated, with newly serviced industries, and industries with poor service, getting priority.
(4) Ideally, price competition between companies, where by some mechanism, a company can reduce their price on a cargo link from the default for a period of time, and hence get a greater amount of cargo over their competitors.
Edit: but these are probably the sorts of things that were discussed when cargodist was first created, and were simplified into the current system