[Ulzgoroth]

Fundamentally equipment costs (in terms of money) aren't balanced as a rule, so the real question is what it needs to cost for your setting, not what it 'should' cost in some abstraction.

That said, things like Psychotronic Generators do put a systematized dollar value on what's essentially a Gadget.

And with a little wiggling Low Tech Companion 2 would cover a Naginata with a full-size added spear head...not that there's much benefit to that pairing.