Therefore someone running a ship will be an employee, or paying off a debt, or in some other situation where the important thing isn't "How much did it all cost?" and "how much does it all weigh to the nearest kilogram" but "how much am I spending / making right now?"
Therefore there is really no need for me to include complicated spaceship design rules for the Weinbaum thing.
What I'm thinking of, instead, is a range of modular components (e.g. "Engine compartment with three engines", "Six-tank fuel module", "Cargo bay 25 tons", "Crew compartment for 2/5/10 crew", "passenger compartment (luxurt)", "Wings" etc., each acting as some sort of performance and costs multiplier. E.g. Wings give your ship the ability to glide to a landing in atmosphere - you can't land on a world with an atmosphere without them - but they add to running costs and reduce acceleration. Fuel tanks add to range but you have to have a full load of tanks or the whole ship is unbalanced, and they cost money and reduce acceleration. More engines add to acceleration but put up the costs big-time. And so forth.
So you start off with a basic running cost of say $100 a month (why not?), look at all your components, and multiply the modifiers together to give a final running cost and performance. If you actually want to know the original cost of everything, multiply the final running cost by 1000.
The idea I have here is to have all of these components in printable deck plan form, with the cutouts fitting together mostly end to end but also on the sides. E.g. there will be basic engine pods similar to the picture I posted yesterday with one, two, or three engines, a fuel tank pod with separate tanks (and possibly an option to add external drop tanks or something, wings, etc. etc.
I'd also have small playing-card sized versions with the values for referees (or players) to use to design ships.
Now, this is such an obvious idea that I have to wonder if there's already an RPG or card game that uses it. Anyone know?