You cannot get UNIX ! At least not like you would get windows ;-) Unix is truely an operating system and a registrated trademark, but you would never find it in a box link windows.
Many hardware vendors did implement Unix for there workstations and servers. I can think of IBM with AIX, SUN with Solaris, HP with HPUX, and lot's of other, and recently Apple with Mac OS-X.
If you buy, for exemple, a SUN Workstation, you will automatically get Solaris Operating Environment.
You could truely install Solaris or other UNIX's on your PC (only Intel processor), but I would not advise you to do that, except to learn something (or to support your customers).
There is a very well known "Unix-derivate". It is not UNIX, but it is based on the same standards (POSIX) and has been entirely rewritten first by Linus Torwald and then by a very enthousiastic community :
Let's go Linux !
It is very intuitive, even with 0 knowledge of Unix you could get a system up and running... and it is fascinating. You have a lot of distribution you could buy for less then 100$ or download for free.
Kind regards !
Laurent