Went to Microsoft.com, searched for Office, found a fairly big button that says "get as a one time purchase", clicked that, followed a one click trail to this page:
http://office.microsoft.com/en-gb/buy/
Note that prices are in pounds because I'm British and the MS site geotracked me to the UK. You will probably get your local currency.
So yes you can get it a single purchase old school style.