Ill take 24V.

That means you need a 2 stage gearing of 13.5-1

I can already tell you, a simple single stage but custom gearbox with aluminium gears suited for a feather, without a motor, is approx £40.
And thats not even commercial, but a price between roboteers.

Imagine a 4 times higher price for each. At least, for a heavyweight robot.