Unfortunately your question is too broad to answer. The price ranges from free for many versions of linux or bsd that you can download to millions for licensing a commercial-grade unix on a large server farm. And the scope goes from a PC or laptop up to servers with hundreds of processors in them. Unix can do about whatever you want, it depends on your requirements.
Search this website (particularly the faqs) and you'll get lots of info. If you have a PC you can spare try downloading one of the more popular linux distributions and learn by using it. As a starting point, you could look at
http://distrowatch.com/ which is a website that lists linux distributions, news about them, and info on how to get them. It may be a little complicated at first, but by reading it and following some links to info that interests you you'll get up to speed pretty quick.
Good luck.
04-30-2006
Unix Cost and the scope of the system
