Think I've caught a butter-finger here. In the table, for the last 2 levels the costs for stone suddenly jump by 2000 out of nowhere. Less subtle is the fact that the wood cost increase slows down. If you check the Timber Camp page, you'll see the source of the funny values: The wood and rock values for the final 2 levels on the Quarry page are transcluded over from the Timber Camp page. Who knows how long it's been around too.