I know I've run it already, here. However I have also run the cost per ton of cargo for small craft as well here you don't need any cargo fancier than hydrocarbons to break even on short trips in canon and that's one way. The S7 can be profitable with hydrogen it can crack out en route from ice it picked up.
The goal was to show that a vessel using Foot Infantry Bays had more flexibility. A vessel with Quarters and designed for 100 days when traveling a shorter route will have at most 9.1% of its capacity available for cargo (.5 tons / 5.5 tons). A vessel with FIB for passengers on a shorter route can have as much as 96% of its capacity available for cargo (5/5.167). As the length of passage increases the percentage available will drop.
So assuming a Dropship has 6,000 ton available for Passengers, Life Support, and cargo. A single person might need 6 tons total in either mode (1 Steerage Quarters + 1 ton of Life Support, vs a FIB of 1/4 of a ton and 5.75 tons of Life Support. (I went with 1/4 of a ton to make the math easy). At 6 tons per person, that is 1,000 people being carried by the Dropship. Then something happens, where the ship's Captain decides that only 50 days of Life Support is needed. The Dropship with Quarters will take up 5 tons base plus .25 tons (50/200) of Life Support, leaving .75 tons per person or 750 tons total cargo empty. The Dropship with FIB will need .25 tons per person plus 2.5 tons (50/20) of Life Support, for a total of 2.75 tons, leaving 3.25 tons available per person, or 3250 tons of cargo.
For costs, I will be using the ones from Tech Manual, p293:
Infantry Bays: 15,000 C-Bills/ton
Steerage Quarters: 5,000 C-Bills each
So if I am using a Passenger Bay of a quarter ton, that is 3750 C-Bills in Manufacturing cost per person being carried. Putting the same passenger in a Steerage Quarter will cost 5,000 C-Bills. If I am allocating more than 1/3 of a ton to carry a passenger in a Bay, it would be cheaper (but larger in mass) to carry that person in Quarters.
The first link with the Dropship comparison spreadsheet, I could not find a way to compare the two Dropship designs (one with Quarters, one with Foot Infantry Bays) for varying mission lengths. Off-hand it looked like I would have to manually change the 'Endurance' on the "Vessel Details" tab, but also change the 'Days' value on the "Fare Calculator" tab. (Go to the first link in your post to see what I mean.)
One idea for a better Dropship comparison might be just showing available tonnage for the Quarters, Bays, and Life Support. From there the player would input how many of what type of Living situation the passengers would have (mass per person in Foot Infantry Bays, # of Steerage Quarters, # of 2nd Class Quarters, # of First Class Quarters), number of days you want the vessel to last, and calculating these masses and costs (the rest of the Dropship will be identical). This way you could have multiple columns where the designer plots how many Quarters/Bays/days the Dropship is expected to support, and if those requirements take up too much room or leave enough space for other cargo. From those values the designer can see what provides the most profit or comfort for the mission.
For example if I am allocating a half-ton 'Bay' per passenger, those bays will have a Design cost of 7500 C-Bills each. But if the trip is short enough, can I fit enough half-ton Bays and charge a decent price to make up for the mass taken up by the cheaper Steerage Quarters?
