I am an electrical contractor in California and I definitely shoot from the hip on every house I do.
You're right when you state that you can never be sure of where material prices are going to go. We do large tract projects of up to 1,000 homes in a single project and our standard contract states that our prices are valid until May 31st. (That is when our union labor wage agreement ends.) This can mean that on some projects our prices are good for a year or more. When prices fluctuate the way they have been it can really cause some anxiety. Fortunately, our contract is simply stating that for every house that we do, this is the price that we will receive. It does not state that we have to do every house in the project. When the wire prices went through the roof this past year we had to request a price increase. If the builders didn't agree to it then we just didn't do any more houses in the project.
When I asked about "Shooting from the hip" I was referring more to the question of does a contractor know what their actual costs are at the time that they estimate the job? When someone estimates a job, do they complete a take-off from the blueprint? Do they red line the print to make sure that everything is included to pass inspection? Do they take the construction factors of the home into consideration? Do they know what the exact material requirement (material list) is for the house? Each device has different material and labor associated with it. A recess can light with a baffle trim has different material and labor than a 3-way switch. Are there high ceilings, does the house have dimensional lumber in the ceiling of the 1st floor that needs to be drilled or are there open web joists? There are many other such factors in how much your material is going to cost and how many man hours the job is going to take.
I read in different forums about how people price homes based on square footage, per open, going rates, etc. I'm just having a hard time wrapping my mind around these ways of pricing. When the price of wire, conduit, steel boxes , cast fittings, etc. increases, how do you know how much you need to increase your square footage price, per opening price or going rate? I realize that I'm coming from a new construction, residential mindset, but I just don't understand how so many people can shoot from the hip when estimating a job and still sleep at night.
I mean no offense to anyone that estimates their jobs using these methods. We all have our own ways of doing things and that's cool.