Question: I've got a rough concept for a trading game in my head and I can't figure out what seems to be basic math.

My cities / space stations / trading posts shall have the following rules:

1. supply and demand are limited
2. prices adjust according to it
3. players as well as NPC traders drive the prices

So the idea is that if X produces less food than it consumes, then over time the price of food rises, and when it's almost empty, it skyrockets. While Y is a net producer, and the price falls over time. This creates a trade opportunity Y -> X whose profitability depends on how many people run the route - if many people trade Y -> X then the prices equal out.

To ensure that players don't simply collude on hoarding food just outside of X, waiting until prices rise and then selling, NPC traders would jump on the most profitable trade routes to keep price differences and demand within reasonable parameters.

I've thought about storage sizes and how prices can swing, but every formula I come up with fails some simple tests. For example, if the total storage of X is 1000 units when the player arrives, he can just buy 500, wait for the price to rise, then sell it again - profit. Obviously, that shouldn't work.

I tried several searches both on Google and here and on Gamasutra and while I found some ideas, I didn't find what seems to me should be a simple formula.

Answer: 
I assume the Geneva Convention bans creation of Cold+FaZe... fire one of those straight down and suck the heat out of the Earth. True genocide weapons. So I'm going with:

FaZe+Lifeforce (FL) or FaZe+Hunter (FH)
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FL is the only combo that is both offensive and defensive. It means your archers can potentially survive area strikes from napalm or white phosphorous as long as they've made at least one kill. If tech army lays waste to an area, they aren't expecting an attack from that direction, so it gives huge surprise bonus. This is my favorite if you're fighting a ground war. 

The problem is airplanes. For these, FaZe is a must. Hunter is the only way to reach airplanes. So, by necessity, that's your combo for an air war.
Personally I think that an explosive and cold combination would work as it would freeze and explode the target. Meaning no restriction of target meaning movement would be less restricted by barriers and the target could be both human and robot.