Let's say 1/4th the cost at $25K that's still $25 trn. Even at $10K per house which is impossibly cheap, that's still $10 trn, an astronomical figure in it's own right.Maybe things were built at a cost less than that
For comparison US has 15 million empty houses which is still a huge number. I'd reckon the figure is more like 50 million for China, which is quite reasonable for their populations and size.