To me it is a matter of how you view your own integrity. I think it would be pretty low to just send him a bill for 20 grand. If you want to renegotiate that is your choice. My own standards of integrity would have me just doing the job at the price I quoted and never saying a word. It actually sounds like you won't really lose any money anyway, you just may not make any but you were the one who made the mistake. He did nothing wrong. You should have been more careful and thought it out better before you did the quote. I have had jobs where I barely covered my material but just put it down to an investment in my education and made sure I learned from my mistake. When I read something like this it reminds me of a job a few years ago. All I really do in the landscaping part of my business is hydroseed by the way and I did a quote on a job and my customer mentioned there would be an area across the drive that needed done. I guessed what he would need and when I pulled in with my hydroseeder the area I thought he wanted turned out to be 1/4 of what he really wanted and I was going to be lucky to break even. I did the whole job muttering under my breath what a #%%^^&^&& this guy was but did it and said nothing. When it came time to settle up he said he thought the area across the road may have been bigger than I expected and he was adding $ 1500.00 to my quote for it. After all that muttering he turned out to be a first class guy. Still, if I say I will do something I just do it. Another story, In another lifetime I was distributing some products. A good customer from 100 miles away called and said he needed a set of $ 45.00 tire chains and needed them by Monday. My salesman who took the call said "I will have them to you by Monday if I have to drive to get them and bring them to you myself. Well when my salesman called our chain supplier he found the only way the customer could have them on Monday was if he really did go and get them and drive them up himself. My salesman was saying what should he do. He felt he couldn't drive 200 miles in a snow storm for something he would make about $ 2.00 on. I told him he should learn not to promise something he was not willing to do. He should have just said he would do all he could to get the chains to him in time. Personally that is how I feel about what you said. You should not have promised something you were not willing to do. Do the job, bill him what you promised and learn from the experience. Be a man and be a man of your word.