RadioPet,
Many of us have made the same mistake that you are considering jumping into right now...that is adjusting your current price for the "I have more work for you later if this price is good" customer. You have been in business long enough to know that this is standard operating procedure for general contractors. A question that commonly gets overlooked is what happened to the last electrical contractor for this GC? Did he make sooooo much money that he could retire? Or could it be that the GC helped him into early retirement in another fashion?
As everyone has stated, your price is too low...way too low. With just the items you have listed and the nm to go with it, you have around $8,000 in material. Plus there are plenty of things not listed. I'm sure you will have a ton of smoke detectors, a few AHU's, pool pumps (a house of this size will probably have a panel at the equipment pad), exterior lighting, ect. These items that are not spelled out before the work starts will be a problem later. You may have the wrong wiring (or none at all), and you will lose productivity by trying to hunt down the proper information.
If the contractor wants a deal and you are interested in working for him/her, propose a discount amount from your regular, profit minded price. When you reach an amount you both are comfortable with, suggest that on all future work, a certain percentage discount will be given until the agreed upon price is reached. There is no reason that you should take the risk of giving a discount up front and not getting the future work. He is not doing you any favors by letting you work on his home, it is a mutually beneficial business arrangement, so I don't suggest the discount at all.
I am sure this contractor understands how job pricing works...from his point of view..."how can I get them to reduce their price so I can make more money? Before agreeing to a price, by all means speak to his other subcontractors (the owners) to see how long they have been working for him and how quickly he pays.
At the risk of rambling on, I again would ask you "what happened to the last guy?" It is a very important question that should be answered to your satisfaction BEFORE signing an agreement with this customer.
I'm sorry for the long post, and good luck, I hope it works out well for you.
Rich