I really think the largest problem here isn't even price, or necessarily opportunity cost. It's that we have this vast, multi-levelled market...and we're handed a grand total of three things we can buy. I understand why you're doing this this way,
@DragonParadox, truly I do. But in an interplanar metropolis I really don't see it as reasonable. Something that might work better here is a system designed around us listen what we'd like, and then you roll to see if we can find it in the same way as you've did for spells in Molten Skies. This leaves us the freedom to pursue what we want, and means that one of strands of major salt here can be resolved for the future. We don't have to go hunting for every single scroll by hand in a magic shop, the same rules should apply in this sort of situation.
We give you a list, you roll to see if we can find what we're looking for. We can then produce a table for you to roll on to alter the price to varying
reasonable degrees, based on if they're native to the plane or not. I'd really,
really try not to go full bore on the simulating interplanar economics, it'll just drive the entire board insane. So for example, we're in the Plane of Earth and decide to go looking for a Griffin. Griffin's aren't native at all to the plane, but we're in an interplanar metropolis so there shouldn't be any major modifiers to chance to find.
Let's say we find some.
Roll a dwhatever to decide how many are available based off of the animal being an extraplanar import. Then adjust the price by a random amount (upwards) between, say, 100% and 200% of its standard market price. This allows for some degree of swing in prices, but nothing too enormous given that the 200% boost will be
rare. For goods or creatures native to the plane, you adjust the price along the lines of 70-120% to take into account supply and possible demand for general trading commodities.
This is clearly a very basic system, but would a more polished version of it be something you'd be amenable to using? Give us the freedom to go shopping, then roll to see if we're successful. The random nature of what we find when we're spending hours walking around is really getting to people, I think, and this would at least solve that. Tossing in a general structure for price variation would probably help work things through too. And obviously, yes, this will have to apply the other way to
our goods too. So we give a list of general 'things from the Material' that we've given and if we're trying to directly sell it you alter the price between percentage points, but given we usually ask what is valuable we'd generally be rolling for a gain of some degree.
Would this suit people?