Me again. ('ello Self)

In RLM's review of TPM, he goes on and on about "space supplies." Which got me thinking how realistic interstellar trade would really be. I guess all space travel based science fiction has to deal with this to a degree... but in the real world, it costs A FREAKIN' TON to launch a rather small amount of matter into orbit. So... take a $1 cheeseburger from your favourite haunt and mail it to someone in a 3rd world country for the low cost of $100,000. Kinda makes the proposition of finding a good hamburger locally "fiscally responsible."

What I mean is: How much better does Harvest Planet X or Mining Planet Y have to be at providing these materials before the cost of exporting them is actually worth it? Can you mail a bushel of grain across the galaxy and have it arrive cheaper than the local grown stuff, no matter how hard it is to grow there?

I ask, because it would seem that one motivator behind an intergalactic war would be to control all of the resource producing planets (environments) which are needed to sustain life/growth/military across all of your other planets. But does that even make sense?

The only way it does make sense is if you assume that transport costs are practically nil. Of course, that goes back into this conversation I was having with myself earlier (in this very thread!) is that transportation or "space geography" based warfare sort of needs to have "travel limitations" to make any sense.

Does that make sense?