A main building company would almost certainly provide a detailed and properly scheduled, quantified price. A professional estimator normally carries this out, most likely using generic estimating software to give an accurate cost base.
Unfortunately, the type of costing software used for this purpose can be a bit rigid in its data input requirements. As a result, the document produced ends up looking more like a major book manuscript, than a schedule of work. Also, being so large and ultra technical, makes it very difficult for any layman to digest.
This cost of this process has to be covered of course. And when all things are considered, those companies will probably only get about 50% of any work they price. The cost of all the abortive estimates has to be included within the company overheads for the contracts they do get awarded. This is a perfectly reasonable position for them to take, as there are no free lunches in this life.