For starships, I think I'd use "service life" as a guide to maintenance costs and fair market value. For instance:
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Basically, a ship will have a chronological age and a service age. Usually, they are the same, but a particularly hard period can increase the service age.
Two points, one dealing with this post, and one dealing with another where you assert that ships should last a very long time because of existing maintenance costs (paraphrase).
Firstly, I'm assuming your maintenance costs are based on the assumption of maintaining original service levels. This might or might not be true. Imagine a nice luxury liner. As it ages, if you kept it up, it might look as good as the day it rolled out. If not, the drapes may get threadbare, the mattresses flat, the lighting may be dodgy in places, and it may eventually be useful only for colonist transport where it used to run first class passengers. My point is that you may, in fact, not have to pay this full maintenance value and the ship may still work fine for a purpose and make 8some money. If you've got it paid off, the profit you can make from it may be more important than keeping it up (based on how long any one person can reasonably operate a ship without retiring or doing something else).
I'm also assuming your maintenance costs don't cover SLEPs which upfit to current tech, just maintenance at existing levels. Some of these SLEPs have a high capital cost (as you suggested). But some, in the real world, do not cost all that much because they use COTS technologies and actually *reduce* ongoing maintenance costs (both because their parts are cheaper and because they are more reliable and robust). So not every SLEP is a money losing proposition. Sometimes, it actually *makes* you money to upfit a subsystem - due to reduced maintenance costs.
So there are several ways to conceive of not following your model that make some sense in the larger scheme. So old ships don't have to bankrupt smaller guys. Past a certain point, it may also be possible to get used, 2nd hand or scrapped parts - if people start scrapping your class, you may be able to get used parts cheap if it was ubiquitous.
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Second point: They're phasing out the F-117 after 20 years in 2008. Why? One of the major reasons is it was manufactured using standard parts for F16, F18, F14 and F15 (landing gear, control runs, etc). Since these aren't in production, their parts cost is going up and up. Newer technologies have actually made replacing it *more economically viable*. So a scenario like this could come up with ship classes in the Imperium - new TL makes old TL stuff not worth maintaining. Or maybe changes in large scale purchasing for ship type A mean that ship type B looks more attractive and A gets phased out long before you'd think it should. In this case, it is also that parts got very expensive.
Of course, you've also got restorationists still flying DC-3s and restoring other old warbirds and planes. And they've brought some Hueys back into service because the Blackhawks are all busy and they needed the air transport inside the USA.
So what I'm getting at is that, although I like your model, one can well imagine several fairly different views of longevity and maintenance expenses. I think one tabular view ends up being only one of the possible routes/cost regimes.
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One other point about the J-4 vs. J-2 comparison: The game doesn't model the cost premium for cargo or passengers for one jump J-4 vs. 2 J-2s. There may be many passengers and cargos that would pay more for these services (as your analysis says they should). The cost of a ticket should be determined by distance, particulars of destination and source, and the rate at which you need to move between. The J-6 may be much more expensive than 6 J-1s, but if you're getting the news to your corporate HQ that Lucan blew off Strephon's head and all hell is about to break loose, you really will pay the extra premium. (Even for less extreme examples, high speed cargo and passengers should exist and don't in the current system). In fact, some passengers and cargo may not even FLY with slower ships (unless no other option is available).
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The other part of cargo costs is competition (you had a reasonable discussion of this): If you're in a 'low trade' TU, your tramp freighter may be the only ship going between A and B that week. If the planet happens to have a glut of people wanting to go (impending war, annexation by the Imperium, you name it), then suddenly you can hike your prices through the roof. At the same time, if you just happen to arrive there the same time as a 2,000 ton freighter on its way through, you may get no cargos unless you drop your prices to below sustainable levels (ie take a loss). In a 'high-trade' TU, there may be so much cargo moving about you don't need to model what cargos you get or passengers very specifically, just what the fluctuation for the week is since there will pretty much always be cargo and passengers far in excess of what a PC ship can take. No worries about being empty.
Someone suggested just rolling % of standard rates. From an RP perspective in a high trade environment, that might make sense. Apply mods based on competition or current campaign events and you'd have quite a workable system that even makes some sense.
You did suggest that cargo wouldn't be carried below cost. I don't necessarily agree. Sometimes businesses elect to take a loss *in the short run*. Competition or a lack of demand may force situations on small ship captains where they have to reduce prices below costs. Can they keep this up forever over the long run? No. But they may be able to endure it for a time (put off that annual maintenance or try to do it on the cheap with aftermarket parts from a boneyard... don't pay the crew fully or on time... dig into the contingency funds hoping for better situation at the next port... etc). So your economic model shouldn't assume that fluctuations below sustainable rates are not possible. They happen quite a lot in competitive environments. And of course, this explains why some companies go belly up - they gamble and they don't get the long run upturn they need to make ends meet. In some cases, I think they hit one of these downturns and they have no idea how to get an upturn, but just keep going hoping a miracle will fall from the sky - this seems to have been the pattern in a few companies that went guts up in the last 10 years that I know of. So I can conceive of it in a TU easily enough. This sort of consideration should be included in an overall model of pricing of services.
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Ultimately, I want my PCs to not have to conduct adventures in accounting. I also want to keep their net cashflow enough to let them buy some good gear, sometimes to spend some doing fun stuff, and sometimes having to deal with unexpected expenses. Enough so they can't just retire ridiculously rich (then why would they be out on the fringes?) and enough so that they can afford whatever supports the story - be it being bankrupt and needing to take a dodgy op to pay for a new jump field regulator or be it having enough money to buy some combat gear for a merc operation. I don't think, unless you are really gaming the economic system, not the general RPG flavour of Traveller, the system's detailed economics can dictate player's actual economics.
I agree with your premise that the game world economics should work (because then cargo and ticket prices make sense). It's nice when they do and when some sensible people have put some good thought into things (yours in this thread, Chris Thrash in GT:FT). Ultimately, RPG story reality dictates more about ship expenses and income than anything.
YMMV, thanks for your good ideas.
