In reply to madmallard:
A cost breakdown is the realm of estimators and systems that simply do not exist among residential contractors. That's what makes them residential contractors.
Only commercial contractors (accustomed to itemizing for government projects, insurance projects, etc) approach estimating that way.
Residential contractors use WAGs, SWAGs, lump sums, square footage estimates, or day rates. None of these estimating methods ever give them the opportunity to separate their labor from their materials. They price the job according to what others are getting (to the best of their understanding, from a conversation with the guy at the supply house), and they do not spend more than 30 minutes or so working on an estimate (the initial meeting with the customer). Anything beyond that, is a waste of time, because it is extremely rare that a customer looking for more detail will ever hire them.
Some contractors, like masons and roofers, simply charge for their labor the same amount as the materials quote from their supplier. If materials go up, they get a pay raise. They have no idea how much time it will take, or what the word "overhead" means.
So, what you are looking for is available, but it will be the contractors more familiar with commercial estimating. These are the same contractors who will be the highest price options.
I realize it is counter-intuitive, but it is true. I am just trying to help.
If you want a low price, you have to figure out how to communicate to the contractor that you are going to be an easy customer to work with and he will make money. YOU CAN'T DO THIS OVER THE PHONE OR ONLINE. Asking for a cost breakdown signals him that you will be shopping it around, checking every stupid detail, and be beating him up on price. It scares him, because you are probably smarter than him. That's not good for him, so he pitches a high price over the fence (which he spends very little time on) on the off-chance you may hire him.
This bothers many owners, but it is the way it works. The reality is that low priced contractors (residential) can't do a cost breakdown. They don't know how. If they did, they would be commercial estimators, and would no longer be low cost.
The only time costs are shown is when a contractor is hired on a cost-plus arrangement. Owners hate this, because they think the costs will run out of control (they are wrong- it's much more fair, and the only way to save money).
The smartest contractors out there will take advantage of you in a cost breakdown. They will give you want you think you want (a list), but it will be disguised, and profits will be hidden all over the place. It will be detailed enough that you think you can understand it, but confusing and vague enough that they have plenty of wiggle room when the time comes to actually bill you. That's how insurance estimating works.
My advice is to consider it less of a list of what you want, and more of a game of psychological advantage, salesmanship,
We don't ask for cost breakdowns when we buy a car, a computer, hire a housekeeper, or buy a steak dinner. Why do we think it is appropriate when asking for construction services?