Earth can be as high as 15g each on the multiple realms I play on.
That said, elementium is 30g where I play (or less) and you can buy it in mass bulk. I routinely drop 5000-10,000g on ore, prospect for hours at a time.
Did you know you can VENDOR all green gems for 5g uncut each? Every prospect, at a minimum, you get 1 green gem. So bare minimum, you can vendor your stuff for 20g and you paid 30g or less from it. And in reality, you average at least one blue gem per stack, and often proc multiple greens on prospecting. Sometimes one prospect even gives 2 greens and 2 blues, I love when that happens.
Now I rarely actually vendor the green gems, generally zephyrites I'll vendor since I can hardly sell cuts on the AH. I make rings/necks out of the rest (and fist weapons). When you make those rings/necks they are green items but have a decent chance at procing a blue item. I sell the blues on the AH for 100-400g a piece, I disenchant the greens. My entire process is much like the old "saronite shuffle". Now the hard part is dust is near worthless on my realm, like 1.50 a piece so its possible to lose money on dust, but essences are worth 40g average so I generally make gold on the disenchant game, plus the blue necklaces and rings make it worth it, I sell like 5-20 of them a day.
Haven't tried pyrite myself, with elementium averaging 27g a stack and me buying hundreds of them at a time, I couldnt see myself dropping 200+ gold per stack on pyrite just to get some volatile earth out of it.
edit- I know they are dropping vendor prices on gems in the future though, so careful of that if you read this 1 month or so from now. I think I heard they are dropping to 90 silver.
Edited, Jun 6th 2011 10:08am by mikelolol