Anytime you show a customer any sort of emotion, you lose.
That said, IMO, the best thing to say would have been:
"I'd be more than glad to clean up these beautiful cars for you, however, being a perfectionist, I would like to restore the finish to better than they were delivered new. However, if you have a fixed budget of $1k, I will be glad to work with you to stay in that realm. Lets talk about particular issues you have with each car and I can offer my approach and approximate time. If you would like to scale those services back, I'm more than happy to, and since you are asking me to do three vehicles, I am offering additional consideration since you are saving me travel time."
That way you appear flexible and you also jab him a bit like he might not be able to afford more. Either way, win-win. You either do the job the way you wanted to or you have a whole lot less work to do.