That does not seem like a great deal to me. If that's $1450 Aussie dollars, that's not that much less than what I have in my Nitron Track double clicker with remote hydraulic reservoir, remote canister, and full Ohlins super bike rebuild for the front forks. I had to pull the forks and ship them, and swap the rear shock, but....
I would also say that it's very possible to build a very nice performing shock using some OEM components. I would not say you'll build a great one using an OEM xx unit, but stranger things have happened. Having played with these and other components, one thing I am absolutely certain about.
There is no possibility IMHO that an OEM XX shock can be made to equal a really good Ohlins, Penske or Nitron. Again, IMHO there are simply no "equal" "good parts" to be used to make them perform the same. There are simply tons and tons of differences. Shaft size, length, stiction, valving and metering, gas charge - all kinds of stuff. If this was not the case, don't you think that top racers would be using these? At least some?
That doesn't mean you "need" or would necessarily even notice the difference. Who knows. I know my suspension at this point is far more capable than I am as a rider.
I have no idea what the shop you're talking about is doing. All I know is that if something is that much cheaper to get the same result, there's probably a reason. Other places would not allow themselves to get constantly undercut if they could provide the same results for less.