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: 
FaZe+Hunter
-----------

Similar to or replacements to modern weapons:

```
Explosive arrows: As you said; like an RPG.
                  best used for AOE/damage multiplier, possibly armor piercer

Combustion Arrow: Use as incendiary and/or anti personnel round

Multiplication arrow: shotgun replacement

```

Unusual arrows with effects possibly worth looking at:

```
Lifeforce Steal: Unless the archer is able to ramp up to truly superhuman
                 speed/strength for a decent period of time this effect is really not
                 worth getting. How many people can one archer kill before someone
                 shoots him or the effect wears off? If it lasts a minute, it is
                 worthless. Lasting a few days might make it worth using.

Cold arrows: Even if it freezes a target into a giant ice cube, how is this better than
             setting him on fire using combustion arrow? A kill is a kill.

Madness arrow: How long does effect last? Does the victim go catatonic or does he attack
               his own side? The effects matter when deciding.

```

The truly interesting magic arrows:

```
FaZe Arrow: This arrow can bypass Armor and walls. the only downside appears to be
            aiming through armor or walls.

Hunter arrow "follow the target...will maintain...maximum speed until Target is hit":
              What a great anti-aircraft round! Aim it at a pilot in a jet.
              30 minutes later it catches up to the pilot walking across
              the tarmac and kills him.

```

My answer: FaZe+Hunter.

This will kill anyone hiding in a bunker, in a foxhole, In a tank, behind walls, in a fortification, etc.
You can also kill aircraft (pilots actually), since the arrow does not slow down and will never stop. It may not kill the pilot until he has landed his plane if the plane moves faster than the arrow, but the pilot will still be dead. If you can target someone outside of view, this combo also becomes an ICMA (InterContinental Ballistic Arrow). Aim a few at the enemy leader and his general staff.

If you can see through walls or armor to aim the arrows, you might consider replacing hunter with any effect that will auto-kill or auto incapacitate a victim such as madness or explosive, but I still think FaZe+hunter is the best combo.

Also: The Elfhome series by Wen Spencer has arrows that magically transmute to a beam of light (laser beam) when fired. This would be pretty effective against modern armies, assuming the resulting laser was powerful enough.
US is already developing sixth generation (i.e. unmanned) fighter jets. These, combined with drones, means the aircraft operators will be on another continent altogether. Unless your hunters can break through the physical security of Norad or Langley, and get within physical striking distance of the human enemy, the arrows will be useless.