Heck my problem is that I actualy work in the Logistics business so I tend to like this type of stuff. However I don't want to to be the focus of a campaign. I want to be something that can be quickly done so characters can move on to the next adventure. After if done right or wrong a far Trader can't quite make enough to pay the bills so you need that supplemental income.
As a retired Army Quartermaster, I like working in stuff like Merchant Prince too. However, my bottom line is that
NO BANK is going to finance a ship purchase or build unless it can be shown that the vessel will consistently, without engaging in speculation, produce a rate of return high enough to cover all costs including the financing.
Given that, the costs of a ship have to change a bit, along with how cargo is handled and charged and passenger fees.
I am working on a build system for ships up to 5,000 tons, where the costs for a civilian ship differ considerably from that of a military ship. A couple of quick and dirty fixes do not seem to work well.
As for cargo handling and charges, I am looking at having each Traveller displacement ton of approximately 500 cubic feet equivalent to 5 measurement tons of Real World shipping space, and able to carry 5 tons of mass. Charges will be based on the mass/volume relationship, with high volume/low mass cargos being charged differently from high mass/low volume cargos.
Passengers will be charged on distance jumped, not per jump, longer jumps will cost more.
Costs will go up in some areas, specifically maintenance and insurance, as insurance is not factored into costs at all. The maintenance cost will be 10% of the total power plant (power plant, jump drive, maneuvering drive) package per year, and 1% of the total ship cost per year. Insurance cost will be 5% of the value of the ship per year, based on purchase or build price. Landing fees will be based on passenger and cargo capacity, along with a flat port charge. Larger ships will pay more.
Scouts will be a bit out of the circuit when it comes to costs, as they will have flat landing fee charges, and can get maintenance done at scout bases, along with Class A and B starports. In my Universe, the Scouts handle what would be called Coast Guard activities in the real world, and there is a substantial Scout presence at all Class A and B starports. The increased cargo ability when it comes to mass should make it easier for retired Scouts with a scout ship to make some money for additional equipment, and adventuring.