The cost is $0.00 and it's freely downloadable.
This office suite is NeoOffice, which is described on Wikipedia as:
" ... a fork of the free/open source OpenOffice.org office suite that is ported to Mac OS X. It implements nearly all of the features of the corresponding OpenOffice.org version, including a word processor, spreadsheet, presentation program, and graphics program. It is developed by Planamesa Software, and uses Java technology to integrate OpenOffice.org — originally developed for Solaris and Linux — with the Aqua interface of Mac OS X."Unlike the existing version of OpenOffice suite for the Macintosh, NeoOffice does not require the X11 windowing system and it has the expected look and feel of Aqua interface applications on Mac OS X.
Check out this online review of NeoOffice from InformationWeek magazine.
The magazine reviewer does suggest that the $400.00 you save by not buying Microsoft Office for your Mac could be used for buying an iPhone instead.