I firmly believe that there are almost no situations where a "per opening" price is suitable as a means for quoting a job. Such a figure may be of some use to you - and you alone- after the job, as a means of checking yourself. It may also be a means of finding the "adder" for changes to an already documented job.
For blind quoting, you're nuts to simply count openings, then multiply.
I quote a job by first developing a plan of what needs to be done. This is based, in part, on what I see on the job site and my past experience with the general contractor.
I know what it costs to keep my business running for a year. This forms the basis of my hourly rate. I make my best guess as to the time the job will take, allowing for all the little things that can make time 'unproductive.' Time x rate = the labor portion.
I make my best guess as to the materials that will be needed. I add something for all the wire nuts, saw blades, etc., that I will use. This gives me the materials cost.
Labor + materials = my minimum quote. I might very well add to this figure, depending on the work conditions, the people involved, my schedule, and whether I want the job (or not).
A proven customer- one who has already provided steady work, pays promptly, and knows what he wants- is rewarded by my 'sharpening my pencil' and giving him a lower price.
A final check on my results is made by comparing my bid to those of others. In general, if you're price is near that of several others, you're n the right track. Too low, and you're missing something. Too high, and you've got issues to address.
So far, software programs are severely limited to "known" jobs, of a size large enough that any errors tend to cancel out. For a brand new, one man shop- forget it.