24V, 400W, but that's on the small stuff.
You must understand, EVERYTHING to do with aviation is extremely expensive. Think of a ridiculous price for a part - any part - and add a nought, and if it's for a helicopter, double your answer. For this reason, when an aircraft is scrapped, nothing that can be recycled is left behind.
Landing lights are replaced on condition, which in my experience usually means they are replaced when they fail. Because of the power consumption, they need cooling, which is provided by an airstream flowing over it, probably at a couple of hundred knots. What sort of speed are you thinking of doing?