Patty
a sheet of 2400x1200 4mm BC grade plywood will set you back around $50-60.....and you'll need two sheets to do one door.....plus some hardwood for the frame...
On the other hand...you could get a sheet of 32mm MDF in 2700x900 for about $90 but it'd weigh 60kgs.......failing that a 2700x1800 sheet of 9mm MDF can be had for under $50 I think.
However, http://www.hardwarestore.net.au/Hume...nal_doors.html has the Hume doors in 2340 tall and multiple widths listed at $84....