Does the ability really need to sacrifice the land? It's quite expensive and not that oppressive. This goes for the entire cycle, really.

What?! dude, are you serious? These are spell effects - good spell effects - coming for free on a dual land! Sargasso Sea looks absurdly expensive for a creature removal effect, but I rather suspect it's priced correctly, because it's creature removal that doesn't take up a deck slot, and doesn't even deprive you of coloured mana like Quicksand did.

The costs are indeed expensive, and development might tweak a couple of them down, but overall they look pretty sensible to me.

I wonder if you can determine power level by looking at the man lands, versus a sorcery that would have a similar effect. For example, what would you pay for a sorcery that put a 4/4 flying creature with haste that sacrificed at end of turn? I don't think anyone would pay for that, like on Celestial Colonnade, but would be a fair cost? Likewise, +2/+2 and trample seems fair (if not underpowered) at . Does that mean that for a repeatable activation is also fair? Or is Celestial Colonnade by its very nature an unfair card? Or can one even derive proper information from this analogy? I'm not really sure on any of those counts.

­ for an Air Elemental you can cast at instant speed, every turn? Probably not quite that much, no. But the "Use this every turn" is pretty nice and important part of the cost.

The cost markup for repeatable vs oneoff is incredibly varied, based on a number of factors. Most of them I don't understand, but potential for card advantage is one.

(+2/+2 and trample for sounds familiar: Selesnya Charm :) )

I was trying to cost more on the safe side.
On a side note, does anyone have any good ideas for the WU and RG dual lands in this cycle? I'm not asking for card designs, but places on Earth that fit into those colour pairs.

­ -> Salt flats? Dead sea? (Though that's named dead, sadly) Flooded deltas?

The classic is of course Taiga. But how about Valles Caldera? (An isolated jungle in the top of a volcano. In actual physical earthly reality, not just Hollywood. Though there's better, still more isolated ones, I can't think of the names.)

I really wish there was a term for "Dry forest that has seasonal wildfires". Yellowstone National Park seems like a perfect land... but it's just a forest. A geothermal forest with a volcano underneath it... but just a forest, ultimately.