Hi Wonderland (hmmm... not a movie reference, is it?).
It honestly sounds like you could use some advice and very likely a proper quote from a pro.
Costs depend on a few things:
- where you want wires run, how much of it - video, audio, speaker.
- how much control you want over the various zones.
- what sort of quality level of components, speakers etc. you're thinking.
Do a it more research perhaps, at least have an idea of what want to achieve - a few rooms with ceiling speakers, but playing what?
Do you want a home cinema - what type of system would you like to end up with, what would you like to start with?
I am based in the South Eastern suburbs...