I was reading a forum and someone was expressing frustration with consultants. This person had brought in several consultants to help that person's church determine what to do to install a new PA. The person has been at this for a year and had received so many different answers that this person seemed frustrated in not having a decisive answer agreed upon to present to the church. . . .
A consultant is expected to provide a solution to a problem that has many viable answers. These answers are viable because just like a car, a sound system is made up of many parts. So just like there are many options when choosing a car, there are many options for the final sound solution. That is why the consultants don't like giving pat answers and why like the original thread of the "It depends" noted all of the frustration in lack of decisiveness that he felt with consultants. Every church is expecting different performance specifications. When I was touring, the PA that I had met our specs so it worked in multiple locations to varying degrees of success.
So with the car analogy, there are brand decisions and the cost differences related there. Each brand has different specs involved. Why do some people spec some brands over another? Well simply, it has to do with the concern over reputation. Why the concern? That is how you get your jobs and keep your family fed. Just like my mechanic will not ever tell me to go down to the giant megastore (you folks in arkansas know) to get parts for my car, but go to certain parts companies that cost more. He doesn't want inferior (in his opinion) performance to affect my opinion of him. The consultant will spec and and use stuff he trusts.
Everyone must make their profit. Otherwise they wouldn't be feeding the family. But, where this profit is made will vary from company and such.
Consultants that only consult make it straight. They make money off of their knowledge not equipment. Also, the cost the consultant will charge will also be based on his reputation (perceived expertise). So it is simple. The less the client knows what they want, the more time it takes to figure it out. The more it costs to consult the job. (BTW - this idea works with other contractors in the building trade - hence the reason a good architect is worth it.)
Installation and design/build folks can put that profit in several areas. They have the design/consultant area, they have the equipment area, they have the installation labor area. That is why you can take two bids with two similar systems and get ranges. If you are spec'ing specific equipment, some guys can't get it direct and go through wholesalers, therefore another discrepancy.
One thing that I do to try to get a better feel for an apples to apples comparison is to have just racks and stacks as well as FOH console and speaker processing bid on first. This limits the choices that the people make, allowing me to see what is going on in the bid. Plus, the items above are the bulk of any PA cost. Once I choose the company I wish to use, then I will ask for a comprehensive bid but with the new items separated out.
If I was a small church, I would make friends with larger churches that are doing something similar to your vision. The larger churches will have more experienced staff that can be a valuable asset. I know that in the large church that I worked for the smaller children's rooms were set up with the same amount of equipment that a smaller church would use in the main auditorium. Visit several of these churches and take notes. Most larger church engineers seem willing to help for not much if anything since they already have their day job. They usually won't be able to provide the services nor attention that a consultant can but most smaller situations don't need that to get something usable. But they can tell you what they would do based on their experiences.
All in all, the creating of a PA is like making a car. There are so many decisions that affect other decisions in the process, it is very hard to get the exact same answer from different consultants or installation companies. There are usually several "right" sound systems for a situation and not everyone will agree upon what is the best between the "right" choices. But that doesn't make any of the "right" choices wrong, just different.
My daughter turned 16 and wanted a car. I got her something that gets good gas mileage, fairly reliable, decently safe, and didn't cost much (since statistics show the first car accident happens in the first five years) nor required a loan. It is a good car and it meets the needs to get around. But she wanted something that looked cool, got worse gas mileage, wasn't as safe, and would require getting a loan. It took years before she saw the wisdom of my decision. I was her consultant. Still, I had a choice of many different cars that met her needs. If someone else was consulted, she may have gotten a different car. It would have cost a different amount as well. But I am sure that a good "consultant" would have chosen a car based on similar criteria and not hers. If that was the case, then who was right? The cheapest? The most reliable? All I know is that her decision wasn't. Why? She didn't have the experience to make a good one.