Ouch, that's pricey.
Up here in Qld, I bought a Taylex 31500 litre concrete tank for $4750 delivered and put in to a hole in the ground that I had got dug for it. They would've charged me another $2000 to do that.
That's it, just the tank in the ground nothing else. I still need to get the plumber to install the Maric valve, the pump, and the plumbing to the house.
Up here another supplier can do a 3000 l slimline poly tank for $975 or $815 for a round ribbed poly tank delivered to the local area, i.e. SE Qld.
My guess is that they would be doing a 3000 l slimline poly tank for you.
I don't know your specific situation, but I'd be seeing if it is possible to get it cut out of your build, then add it later with downpipes from one side of the roof to the tank, and just using the tank to water your garden with.
I'm sure SaveH2O will have many more educated answers than myself.
At the beginning they said the water tank has to be installed by them, then today they said I can deduct 3k to install the water tank by myself, since they still need to install the pipes, and pumps etc. i understand they need to make money as much as possible, but the price is really ridiculous. I'll try as much as possible.
Any one has any suggestion regarding this issue?