How sure are you about this part?
The way I understand it (may be wrong), is that the airlines charge them by either volumetric or physical weight, whichever is biggest, and they pass this cost onto us - they can't decide to just not use volumetric. Imagine someone shipping 30KG of polystyrene in a box, it would be pretty huge.
But if I'm wrong, please tell me, because that would be a pleasant surprise.
Only thing I can think of why it'd be that much, is if they do indeed use volumetric weight, and the sender put it in an unnecessarily big box.