THANK YOU! Apparently, we agree that this looks rather uneconomical, bordering on usury, right? What do you think about politely asking the general contractor for an explanatory breakdown of the costs based on a more detailed cost accounting? Why is a 15-GC surcharge justified again?
Another question, what does your payment plan for the house look like? What is that supposed to achieve? He can probably imagine why you want the details. He seems totally indifferent. If you approach him with effort, he will probably just say "No, I won’t do it."