New Gas Line for Instant Hot Water Help?

Hi, I was quoted a ridiculous $2500 to run a 32mm gas line from one side of the house to the other. The reason being the it has to go in the attic and cost of materials e.g copper pipe is very high.
My house is double storey and the distance from gas meter to hot water unit is about 80-100Metres. Can someone please advise if this is a fair price and how i could save money with this.
Current gas pipe is 19mm-20mm and plumber says will not work with unit.
I really want to install this unit but i can't afford the price quoted.
Can i use pvc piping to lower the cost and is this unsafe vs copper piping.
50% of the distance is inside in the house attic.

Also if i was to do it myself e.g buy the materials and just get the plumber to supply his labour. Would this save much or should i ask for more quotes


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