It would be naïve to think that for some who enrolled in their country’s armed forces, money was not a motivating factor. This would have been especially so for non-skilled labourers prior to the first-world welfare of the 20th Century. For professionals who chose to put aside their career, enlisting in the military may have resulted in a loss of income, however for a man who was unemployed, the basic daily payment, along with the promise of food, clothing, and medical care, was a viable option. Just how much money was involved though?
Let us look at an era where the records are easily accessible: the Second Australian Imperial Force (AIF) in the Second World War. The amounts are in the imperial measurements of pounds (£)/ shillings (s)/ and pence (d).
The basic daily rate of pay for a single member of the 2nd A.I.F. ranged from 5 Shillings for a private, 2 Pounds 2 Shillings and Sixpence (2/2/6) for a captain, to 3/3/9 for a Major General commanding a division or equivalent. Married men were paid a separation allowance of 4 shillings per day for the ‘keep’ of their family, regardless of their rank, in addition to their basic pay.
Once a soldier had embarked overseas for an active operational area, the private was paid an additional 2 Shillings which was ‘deferred,’ in other words, set aside for when the soldier was discharged and then paid to him in a lump sum.# Thus a man might have a substantial sum of money available upon discharge.
Other Ranks (non-officers and non-warrant officers) who were classified as a Trade Group Specialist due to their role such as cook, clerk, armourer, motor mechanic etc., received additional daily specialist pay above the basic rate for their rank of private/trooper/gunner etc. This was between 1 and 3 shillings.
An ordinary, single, non-specialist private then, would earn a basic pay of 35 Shillings per week (£1/15/0), with a married man of the same rank receiving his same 35 Shillings plus an additional 28 Shillings separation allowance for his family. At the beginning of the war in 1939, the basic [minimum] Australian weekly wage rates (state awards) for adult males varied between £4/4/0 to £4/ 9/0. Such a comparison with civilian wages can only be a rough approximation, and it must also be remembered that out of that wage, a civilian still had to pay for food, rent, and other expenses, the basics of which were provided to the servicemen.
An unmarried sergeant earning 70 Shillings (£3/10/0) per week with only relatively minor expenses if stationed in a base area such as entertainment money, for example, would be in a financially reasonable position, all other areas in his life being orderly, that is. The exception would be if he had left a highly paid professional career in order to serve his country.
Comparing what an Australian soldier of the 2nd A.I.F. was paid with those in other Commonwealth countries can also only be a rough guide, but the following may be of minor interest.
Privates in the New Zealand Expeditionary Force were paid a standard 0/7/6 per day with 4 Shillings being deferred.^
In Canada, prior to embarkation for active service, a private received the Australian equivalent of 7 Shillings and 5 Pence per diem, with roughly half that amount being deferred once embarked.
The British ‘Tommy’ appears at first to be poorly paid in comparison, with the base rate upon enlistment being just 2 Shillings per diem, however there were a number of additional payments which, when qualified for, raised this amount. After one year of service, for example, the private received an extra 3d (3 Pence), rising to 3 Shillings after three years. War pay of 6d was additional, as were efficiency or proficiency payments, a ‘Colonial Allowance’ for service in certain locations such as Egypt and Palestine (5d daily). There was no deferred pay in the British Army.
Spousal allowances for Australia, New Zealand, and the U.K. were comparable at 3 Shillings each day, while a Canadian wife received6 Shillings and 7 Pence daily. The Dependant Children’s Allowance for Canada was similarly generous at 2 Shillings and Thripence per day, compared 0/1/6 for each Australian child under the age of 16, and the same for New Zealand. In the U.K., the ‘1st child’ received 5 Shillings per week, the 2nd 10 Shillings, the 3rd 12s, and each additional child 3s.
[References are available on request].
# An ‘Exchange Allowance’ of sixpence was also applicable, though I’m uncertain of the details in this regard. Can anyone enlighten me?
* It might be noted that prior to 1940, members of the A.M.F. Australian Military Forces (Militia), were paid other allowances such as camp, field and mess allowances. Pay and conditions were standardised however during the early months of the war.
^ The New Zealand rate was either 7 Shillings or 0/7/6.
Note: The Commonwealth pay details were current as at December, 1940, though on the documents there are corrections to amounts, whether this was due to the currency conversion to Australian pounds, shillings and pence is not known. In other words, the amounts quoted above are approximate only. There are also discrepancies over several documents regarding the Australian rates of pay.

Darren,
It looks like the exchange allowance accounted for the fact that AIF soldiers received some of their pay in Sterling. So it would have been a means to adjust for the exchange rate. This article from Trove discusses some of the rates.
http://trove.nla.gov.au/newspaper/article/46347833