Do you actually mean Unix, or would Linux be okay?
Unix is usually purchased for a high price, but Linux is mostly free.
Sun's Solaris 10 is Unix, and it's free.
http://www.sun.com/software/solaris/This was the first actively developed commercial Unix system to be open sourced.
Unix (officially trademarked as UNIX®) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. Today's Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations.
As of 2007, the owner of the trademark UNIX® is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX®" (others are called "Unix system-like" or "Unix-like").
During the late 1970s and early 1980s, Unix's influence in academic circles led to large-scale adoption of Unix (particularly of the BSD variant, originating from the University of California, Berkeley) by commercial startups, the most notable of which is Sun Microsystems. Today, in addition to certified Unix systems, Unix-like operating systems such as Linux and BSD derivatives are commonly encountered.
Sometimes, "traditional Unix" may be used to describe a Unix or an operating system that has the characteristics of either Version 7 Unix or UNIX System V.
