The "best" way of purchasing Microsoft Office for your needs:

Unraveling the best way of purchasing Microsoft Office for your needs, here is a starting point:

Details and prices correct as of 10/03/15, based on $AU, sources:
https://products.office.com/en-AU/buy/compare-microsoft-office-products
http://products.office.com/en-au/business/compare-office-365-for-business-plans

Office 365 Home $12 month - ongoing (less if paid by the year)

5 PC's from the same "household"
Standard suite plus Outlook, publisher and access
**Non commercial use only
Extra benefits: Skype 60 minutes x 5, 1TB Onedrive storage x 5, free upgrades (while you continue to subscribe)

Office 365 Personal $9 month - ongoing (less if paid by the year)

1 PC only
Standard suite plus Outlook, publisher & access
**Non commercial use only
Extra benefits: Skype 60 minutes, 1TB Onedrive storage x 5, free upgrades (while you continue to subscribe)

Office 365 Business $12 month (minimum annual commitment - ongoing)

5 PC's *for that single licensed user*
Standard suite plus Outlook & publisher
Business use
Extra benefits: 1TB Onedrive(?) storage, free upgrades (while you continue to subscribe)

Office 365 Business Premium $13.86 month (minimum annual commitment - ongoing)

5 PC's *for that single licensed user*
Standard suite plus Outlook & publisher
Home or business use
Extra benefits: 1TB Onedrive(?) storage, Exchange based business email, free upgrades (while you continue to subscribe)

Office Home & Student 2013 $169

1 PC
Standard suite (*no Outlook*)
Non commercial use only
Extra benefits: No ongoing costs unless you chose to upgrade in the future

Office Home and business 2013 $265 (street price)

1 PC
Standard suite plus Outlook
Business use
Extra benefits: No ongoing costs unless you chose to upgrade in the future

Office Professional 2013 $599 (RRP)

1 PC
Standard suite plus Outlook publisher and access
Home or business use
Extra benefits: No ongoing costs unless you chose to upgrade in the future