Well I did oversimplify a bit , they added a DSP and did calibration ( twice , i just returned for my tune-up after the speakers were broken in a bit) and some custom work. I did verify the cost of all the components and they were competitive and as you say it was quite labour intensive. They had the car for roughly 2.5 days to do the installation.
You can likely get 70-80 % of my result for half the money but I had specific goals in mind and didn't mind the extra cost. I went with fairly high spec ie "costly" components as well.
I also wanted an installer with significant experience as I had read in the past of poorly done installations that caused issues with the car. Perhaps not a huge issue at this point as the cars are fairly common now but I wanted peace of mind.