To determine the minimum size of a suitable step down transformer:
The nameplate on the Darex DD750X says "110V 1.75A". 110V x 1.75A = 192VA. I would recommend to go at least 1/3 larger than this. So the step down transformer should be rated for at least 300W.
Like this one on eBay for 34.90 with free shipping:
http://www.ebay.com.au/itm/240v-110v...item565168486b
or this one, more like a wall wart, for 34.99 with free shipping:
http://www.ebay.com.au/itm/step-down...item5af71be424
Of course, except for space and weight, there is no reason why not to go for a larger model. 500W cost $36, 2,000W like this one cost $43 plus about $20 postage:
http://www.ebay.com.au/itm/NEW-VOLTR...item20e7908d26
In essence, one could also use any transformer of 300W or larger from the scrap box, that has a split primary winding (usually 2x 110 or 2x120V). In this case one does not need to hook up the secondary winding(s), and it also does not matter what voltage these secondary windings are. If going this route, I would however very strongly recommend to put the transformer in a properly grounded metal enclosure to protect from metal dust and chips etc. And add a suitable fuseholder for both input and output.
EDIT: Step down transformers were quite common in the 80s and 90's to hook up laser printers, which were back then much cheaper in the US than in Australia.