If we're talking about the hub only, then it doesn't seem particularly inexpensive to me. But it doesn't seem like a bad price, either.
An internally geared hub plus drum brake does seem like an intriguing idea for an MAB, doesn't it?
The question I've always had over it is will that drum brake interfere with mounting the engine drive sprocket? I'd have to find the answer to that before I could give it a try.
But imagine a motor bike with drum brakes front and rear. It does sound nice.