You can purchase Microsoft Office:mac 2011 at best Buy or most office supply stores like Staples, Office Depot. It can also be downloaded directly from Microsoft's web site.
There is a 30 day trial that is available from Microsoft's website.
Like the Windows versions, the retail package (on DVD) comes in a few flavors, but there are fewer choices.
Home and Student is just Excel, Word and Powerpoint and comes in 1 or 3 computer licenses and sells for less than $200
Home & Business comes with Excel, Word, Powerpoint and Outlook and comes in 1 or 2 computer licenses and sells at approx $250 or more.
Unlike their Windows counterparts Office:mac does not have OneNote, Publisher, Access, Visio, Project or anything else I may have forgot to mention.