As seen in sixty second shooter (well, sixty second shooter wasn’t done with Unity but that’s what I originally wrote the Cg code for) and to be seen in Energy Hook.
This shader uses a double lookup into a smooth noise texture to create shifting patterns of clouds or smoke. It’s great for lava lamps, plasma fields, ominous magical clouds, or crystal balls. And you can combine with another texture to create fades, circles, veins, circuitry…
It’s not the most powerful or flexible procedural smoke shader in the Asset Store but I believe it’s the cheapest, at $10.
You don’t need Shader Model 3, but I’ve only tested it on Mac and Windows. I haven’t rigorously measured performance, because I’m draw-call bound. I cn say it does 3 tex lookups, so it’s probably about on par with a bumpy reflective shader - so if you’re GPU bound might not be for you.
I can’t test it (don’t have the mobile licenses) but I don’t see why it wouldn’t work. Also, I believe the Unity store allows refunds, so if you try it and it doesn’t work you ought to be covered?