Marine ply - source and price in Sydney, Australia?

Hi folks, this is my first post to this esteemed group. I'm
hoping that there's a few Australian participants besides
myself who might be able to cast some light on this enquiry...

I've recently stumbled across a couple of web sites with designs
for tiny one-sheet or one-and-a-half-sheet boats, and I thought
I might have a go at making one. There are a couple of gaps in
my knowledge though:

First, can someone suggest what I might expect to pay for an
appropriate sheet of circa 2440mm x 1220mm plywood in Sydney
Australia, along with suggestions as to a source. I looked
yesterday at my local 'Bunnings' (not really expecting to
find anything appropriate) and found that I could have any
sort of ply I wanted, so long as I wanted 600mm x 1200mm
sheets :-/ Locations from the city to the north-east are
most accessible to me. (Some indicative pricings from other
parts of the planet would be equally welcome)

Second, is there some sort of finish that I might apply to a
plywood boat that would provide the necessary waterproofing
whilst at the same time being clear, so the grain of the
wood remains visible?

Third, what type of plywood should I be looking for? Am I
correct in assuming that I must use 'marine ply' for this
light-use application in a small one-person boat, or are
there alternatives that I should consider? Price is more
of a consideration than durability, since my interest is
more in the building than the using!


Thanks in advance,


GB
--
"Most police misconduct occurs when citizens challenge an individual
officer's authority" (Reiss, 1971 c.in Jermier & Berkes 1979)