So could I. But why would you when he's trying to come to a site like this, get someone to bite on an estimate, so he can beat up his EC that's on his job?
Most GC's have a stable of EC's they use regularly. If I was on a job and priced a change order, and the GC went to one of his regulars (my competitor) to check my price, I would get a phone call from my competitor telling me he just got a call wanting this info. My competitor would protect me by doubling what I quoted.
That's why he's coming to a site like this for that info.
Agreed. We routinely have people try to drag us into the middle of change order pricing. "You're the engineer who designed it," they'll say. "Is this change order reasonable? It seems awfully high."
We smile and say we'll look into it, then start grumbling as soon as he's out of earshot. "How am I, as a desk jockey engineer, supposed to know how much the change is going to cost? And if you, Mr. Architect or Mr. Owner, think the change order is excessive, maybe you shouldn't have redesigned the entire job after it was bid."
Anyway, we dutifully go through the change order to see if there are any glaring errors (e.g. we added 10 branch circuits in 3/4" EMT but the CO includes 500' of 4" EMT). If we encounter anything, we give the EC a call to let him know. In my experience, 100% of the time the EC thanks us for catching it and re-issues a corrected change order. It's a professional courtesy, because that way the error gets fixed and the EC comes out looking like a stand-up guy who caught and corrected his mistake, rather than like a weasel who's trying to slip one past the client.
My boss has told me of a few experiences he had years ago when somebody started challenging the EC's price on everything. I'm sure you know the drill: "How can this cost $2000? It shouldn't take you more than half an hour. The total cost should be 250 bucks, tops." The EC shrugged, looked the guy right in the eye, and said, "If it's so easy, you do it for 250 bucks. But if my crew's doing it, it costs 2000." Of course, the critic backed down and the EC got his $2000 (which, as it happens, was a perfectly reasonable price for the work that was being done).
It has been my experience that arguing with a Contractor about how much labor is involved in an installation is a pointless endeavor. He does this sort of thing every day, and he knows what he's talking about. If his bid is too expensive, find somebody else who will do it for less. If nobody will do the job for what you want to pay, you need to consider the possibility that your expectations are just unrealistic. Go save up some more money and re-bid the job in a year.