Okay, I've thought about it, and I'm ready to answer. I'm sure I've used just about every response possible over the years. Some jobs can be guesstimated easier than others, but the real best answer is:
"If you're going to choose the contractor you use to wire your home (not house) based on a number given to you over the phone, I'm honestly not interested in bidding on it. There are too many important details of the job, not to mention the qualifications of the company and the individuals who perform the work."
Sumpin' like that.