A search of Google returns this --
http://www.google.com.au/search?hl=en&q ... DcountryAU
I would try ringing the first on the list,gaspoolheating.com.au, and explain your circumstance.I see they are located in NSW but you would think they could give you a clue or point you to someone who can,especially if you could tell them pool capacity and model of heater.
Cost would also depend on how you plan to use the pool.It would obviously be cheaper to use the heater to just take the edge off rather than get it up to a "heated pool" temperature.
Pools also have a relatively large thermal mass,our unheated outdoor pool once the sun has warmed it,will remain warm for days even if the weather cools down,meaning your pool will also retain its heat and not go cold the instant you turn the burner off.A pool blanket will certainly help.
Just my thoughts,good luck with the auction.