For a comparison of costs, the price for a wagon in the Hub rules is 122-320 silver pieces (avg 221 sp), carries 1200 kg. From :Pitford: Gateway to the Ruins" the fee to ride in a wagon is d6+2 silver coins (1 day trip) (average 5.5 sp). So the price for renting for 1 day is about 2.5% the cost of the item for one person. From there we need a rough idea of how many people per wagon. If there are 4 people per wagon the rental cost is 10% the cost of the wagon. (I am assuming 2 people to guide the wagon and the PCs in the back.)
This gives me a rough ratio of 2/3 the total people will be passengers, and the passengers will account for 1/10 the airship cost.
Looked through the books, and several pieces of data concerning airships at the end of this post.
One set of data is from the Crossroads region Gazetteer on page 28 where it lists the stats of battle airships that can carry up to 27 people. The other piece is from page 157 where it said that the airship headed from Newburg to Overpass would cost is 80 sp per person; has a trained giant bat to go faster (from hub rules p220 this provides 25% of the bat's speed of 20m, or 5m, from the Hub Rules p149).
So an airship can handle up to 18 passengers, each paying 80 silver pieces (I am assuming the higher speed from using the trained bat is offset by the bat's extra food needs). 18*80 = 1440 silver pieces.
So a Battle airship will cost 14,400 silver pieces.
The Hub Rules airship (page 219) can carry 10 people or 500 kg of cargo (each person is fairly small, only 50 kg each), plus 6 people on the upper deck, and 1 on the crow's nest (total 17). Assuming the same 2/3, this means 12 people can pay up to 80 silver per, so the max cost of the airship is 9600 silver pieces. In this case since the bat is not available to pull (no 25% bat speed bonus), this means the airship ticket will be lower, but the trip will take longer.
The airship uses 5 liters of alcohol fuel to keep the lift bag at the right temperature to provide 12+d6 hrs of travel (the cargo capacity will be used for additional fuel as required). From the Hub rules each liter of alcohol costs 21-40 sp per liter (or 105-200 silver pieces per trip)
A more complex equation could be set up similar to the robots, where you purchase an airship's lifting capacity (the main bag), and add structural material, engines, weapons, armor, etc. Higher fraction of weight used means lower maneuverability/lift rate/speed. Passengers will need to consume food, while the gas bag will need to be heated by an alcohol engine (fuel usage per day). Water is not an issue as long as you have a clean exhaust pipe, as the water in the exhaust will condense if engineered properly (and if the incoming air is run next to the waste pipe it will heat the incoming air too). Waste is not an issue for the airship passengers, but is a concern for people underneath.
Airship data:
Hub Rules:
p219 - airships rise 2 m per round (40m per minute, 2.4 km per hour) up to a maximum altitude of 3048 meters (after that the air gets too thin).
Excavator Monthly Compendium:
p57 - caravan is disbanded due to competition from airships (and other transportation)
p146 - airships are preferred when traveling longer routes
Crossroads region Gazetteer:
p28 - stats of airships:
* Transport airships have 3 heavy crossbows, 9 troopers
* Battle airships are cargo and troop carriers, carry 1 light ballista, 3 heavy crossbows, plus a weapon relic for the captain. Operated by 7 troopers but can carry 20 passengers.
p54 - passage from Pitford to Steel Hill via airship, 25 silver pieces, this is a rare cheap flight
p55 - agent costing 200 sp per day can have an airship at the PC's location within 2d6 hrs
p60 - airship 1 km away, symbol on it is visible (so using
this as a guide, the ratio is 25, meaning that for 1 km away the symbol is 40 meters tall, this gives us a rough height for airships)
p99 - airship puts down a "handful" of Purists
p157 - airship headed from Newburg to Overpass, cost is 80 sp per person; has a trained giant bat to go faster
p160 - airships are fitted with 4 muskets each, and are the main cargo carriers between Newburg and North Fort
p208 - Imperial Purist airship with crew of 4-6
p312 - Huge airships have a crows nest with 2 people each with a heavy crossbow, baskets are 2 levels, upper is 4-6 soldiers each with heavy crossbows, and a family for each in the lower level
p363 - Airship capable of moving 9m per round (no information if with or against the wind)
p364 - Purist airship with 6 Purist troops each with a heavy crossbow can get up to 1400m up
p378 - Purist airship can get up to 6 km up (from the Hub Rules, they must be using very thick gear and additional breathing apparatii if over 3 km altitude)
