Yes, thanks for the links, that really helps.
I see a space like that in the pictures and immediately think about factors such as how to get cabling to a new center speaker location, how you would actually attach the speaker rigging to the building structure, determining at what height the speaker can be flown and not interfere with the view of the cross and/or projected image and so forth. Those types of issues could affect the design and the installation cost and would seem likely to require a site visit to assess.
When looking at any rigging it is important to consider not just the proper rigging of the devices but also the proper consideration for who that attaches to and affects the building structure. I am very sensitive to such issues right now as I am currently going through a situation on a project where myself, the Architect and the Structural Engineer for the building coordinated flying the speakers from the main building structure directly above. The AV Contractor instead submitted a considerably different approach to rig the speakers that has them supported from a frame that is in turn supported by the framed walls below the speaker 'enclosures'. Their concept would work fine as far as the frame supporting the speakers, however we have confirmed that the walls they show supporting the frame were never designed for and would not support the associated load. I have also had other projects where initial assumptions on speaker rigging turned out to not be practical once looked at in more detail and that resulted in significant additional costs.
So my concern with someone quoting a cost for installing a flown speaker without having first visited the site would be that while the basis for their quote might work just fine, I can also see the potential of their either trying to 'force fit' an inappropriate rigging solution or asking for a Change Order for more money to accommodate conditions that turn out to not be as expected.