Artifacts, Minerals, or Research?
What are the prices for warehouses for each type?
Explain why.

warehouses are about 500-550ctp each and it depends on where you are in the game for importance for the first 200 levels or so research is the most important (try to bring up mining with costs) and from about then on artifacts become more and more important.

I would think mineral storage would be worth more, 'cause that's the easiest to fill up, and maybe research. Artifacts have much higher natural storage than the others, so I'm not sure there's as much danger of that filling up.

at higher ranks with going for almost exclusivly artifacts they begin to hit cap faster, at low levels it could take DAYS to fill up my artifacts, now it take me 11-12 hours to fill them up with 20K additional artifact storage.

They all cost the same in GP, although artifact towers have twice as much space as the other two. Anyone selling on a trading group would be looking to recoup about the same amount.

Like Sgt. Lynch said, relative importance changes with your rank and production levels, it also depends on how often you can access the game.