A few really good questions here.

Let's start at the beginning. Six shillings a day was about average for an Australian worker in 1914. In the first volume of his Official History of Australia during the First World War, Charles Bean wrote about the pay rate for a private, stating:

"The pay of Australian soldiers and sailors in peace-time was calculated to yield them the same return, when their rations and lodging were taken into consideration, as the average Australian worker obtained in the shape of wages; six shillings a day, although generous, was not high by that standard."

He continued however to state that although not necessarily better then the average civilian's wage, it was definitely a higher wage then that receieved by a private in any other army. American privates received the equivalent of four shillings and seven pence, a New Zealand private got paid five shillings and a British private received a measly one shilling at the beginning of the war (growing to three shillings by the war's end).

In the Australian army, five shillings were paid to the soldier himself while the sixth was withheld to be paid out at discharge.

According to the Reserve Bank of Australia's currency and inflation calculator, six shillings in 1914 would be equivalent to about AUD$37. This doesn't seem like a lot but it was paid daily and remember that the army was paying for food, lodging, equipment, transport etc. It would have been hard on a soldier's spouse however as the soldier wasn't obligated to send money home while overseas until 1915 when two-fifths of a soldiers wage had to be allotted to a soldier's family.

As for a motivator, we don't really know the extent to which money was a factor in encouraging enlistment. We have a few letters in which soldiers mention money being a deciding factor such as that written by Robert Antill to his family in which he wrote:

"One this its not bad moiney here 5/- a day and clothes and food thats nearly good as Cabinet Making and not half as hard. You may thint it funny mee turning up such a good job but it was like this Philpott had only about 3 days work left for us and things are so bad out here for there is a drought on...so I thorrt I would join the army."

As you can see, for Antill, money was indeed a factor and though he was being paid less then what he was working as a Cabinet Maker, the certainty of ongoing employment and pay if he enlisted provided enough motivation of him to sign up. As I said, we can't be sure as to the extent of money as a motivator but Australian historian Joan Beaumont speculates that conditions in Australia in the months before and after the British declaration of war including disruption of the economy and the drought mentioned by Antill led to a not insignificant amount of unemployment, making enlistment and the promise of a guaranteed wage very attractive.

Sources:

Broken Nation by Joan Beaumont

Official History of Australia in the War of 1914–1918. Vol 1 by Dr Charles Bean