Amcal online sells them for $35 a box. If you buy through their eBay site enter CAU10 in the promotions box at check out to receive an extra 10% off.
Chemist warehouse also does price matching, Amcal does have physical stores as well, so you could get it cheaper plus an extra 10% off via CW.
Priceline, Chemist Warehouse etc all have sales on these things every few weeks.
I also like to search eBay auctions, some people buy it don't like it etc so try and sell it for a fraction of the price.
Hope this helps!