I figure I can't go wrong with this Pierre Cardin Shirt for $11.99. I did a quick search and the cheapest prior to this deal on OzBargain has been the Men's Shop @ $28 a piece. Myer lists Pierre Cardin shirts for $80 so even with their 50% off sale, they will come in at $40 each.
Also available are these Van Heusen Shirts for $14.99 - $19.99:
http://www.ebay.com.au/sch/Business-Formal-Shirts-/57991/m.h…
and these Como shirts for $10 each but I can't find any reviews on quality:
http://www.ebay.com.au/sch/m.html?_odkw=&_uhb=1&item=3711078…
Edit: Just found some $14.99 Van Heusen shirts as well which I have added.
I bought this along with some $20 dollar Globe Jeans
http://www.ebay.com.au/sch/m.html?_armrs=1&_ssn=catchoftheda…