What kit were you having installed???
What projector?? What screen??
If it is a dedicated room why would you consider anything other than a fixed frame screen?? Anything else is a compromise. You need to spend 10x the amount to get almost as good.
And 'in wall' speakers?? Again, a serious compromise imho.
My last house had the Kef Reference Custom install speakers, and it was OK, but not a patch on decent DSP speakers.
I am actually goin the other way, just sold my cinema room equipment and going back to having a nice, neat DSP system in the spare reception room, where I know we will actually use it every day.
If it were me, I would get a builder in to do the work you want and buy the kit and install it yourself, you made need someone in to set up and calibrate the projector to get it singing, but that will be small fry compared with the expense of getting a custom install company in where they are taking their cut of every step.