Many collectors seeking to answer this question might nominate Detective Comics No.27 (the debut of Batman), Batman No.1 (the debut issue of the first ongoing Batman title), or any number of issues introducing such iconic members of the "batman universe" as Robin, The Joker, or Catwoman, to name but a few.But it's be fair to say that few Bat-fans would list Detective Comics No.243, published in May 1957, as an exceedingly rare, or sought-after Batman comic. But here in Australia, it seems, that this issue is an inadvertently "hot" item, because it forms the basis for Giant Batman Album No.14, which was published in Australia by Colour Comics Pty Ltd in 1968.
Actually, the Aussie version may have just as likely been a reprint of DC Comics' Giant Batman Annual No.5, published in the (USA) summer of 1963, which also featured the lead story, "The Giant Batman"

For reasons that remain unknown to collectors everywhere, it seems the mid-teen issues of this Australian reprint title (Giant Batman Album), are scarcer than rocking-horse poop. You actually stand a better chance, it seems, of scoring the 1st issue of this series, than you do of issue nos.13-16, or thereabouts.
Unconvinced? Well, today a copy of Giant Batman Album No.14 sold on eBay Australia for AUD$129.50.
Holy Mylar-sleeve with-backing-board, Batman!

