ive been looking at a few batteries in the last week or so
the only brands i would settle for are
century
exide
bosch
yuasa
dont go for cheap batteries
supercheap/k mart/ repco can sell these to you
cheapest bosch one i found was at supercheap auto for 140, and if u trade in your old battery u get $15 bucks off.
the specs were 13 plates, 600 cca, 115 RC, its big, should be able to fit in.
kmart have got a lot of exide batteries and there all at a reasonable price, for around $110 u can get an 11 plate 550cca battery for that
marine shops would also be a great place to find deep cycle as far as i know thats all they use
caterpillar australia also sell batteries, but there damn expensive, my bioss said he had one, and it lasted in his car for 5-6 yrs, pretty much double the life of a normal batterie and close specs to the first batterie i mentioned (bosch), but will cost around 200.
anyway theres a heap around, and everyplace tends to sell them for different prices. so best bet, would be to get the most amount of plates (11-13), highest cca (cold cranking amps), and rubber casing which most deep cycle batteries have
hope this helps!!!
-Cam