10kg of steel would cost about USD$10.00, and then shipping it around the world costs again. At my factory, we use the number "50 cents a pound" as an average cost for shipping pallets around the lower 48 states.

So your extra 10 kg would cost me about $20 more. At retail that would be another $100 or so. In other words, making it 10kg heavier would sharply increase the price; it would also be for things that aren't easily visible to the consumer. Your competition would destroy you.

Source: I own a factory.