I have a kineticist player who really wants/needs an item to help his character out.
I'm not too well versed in the class, so balance may not be achieved with this idea, but I was looking into old warlock stuff from 3.5 and the Rod of Eldritch Power seems to be able to translate into the class pretty easily.
Substance and form infusions more or less equate to essence and shape invocations, and the different levels of invocations (least, lesser, greater, and dark) seem to scale similarly to burn costs from 1-4.
Would simply converting the item over be something good/balanced for the class?
Prices: 4000, 8000, 36000, and 64000 for each level respectively.
There's a couple of small issues that might stand in the way. First is the fact you need to have both hands open to gather power (not counting items used with a telekinetic blast), so your version of the item would need to allow gather power while it's held. The second is figuring out how it'd work with kinetic blade, kinetic fist, or kinetic whip. Otherwise, though, it seems like this would work perfectly, perhaps with some tweaks to pricing to allow it to scale for 9 levels (especially if you're including 3pp), although your idea of least > 1, lesser > 2, etc. works well enough in a pinch.