I am looking to start on online magazine and I don't have a special name for it yet, and I am intending to monetise it through adds. I found a good domain that has a PageRank of 6 for 600$. is it worth spending this amount of money for it ? I mean does it adds some value to the website ?
There is no such thing as a PR6 domain. Domains don't get PageRank. Pages get PageRank. That PageRank of 6 only would apply to the home page of any website using that domain.
It's not worth it because PageRank carries very little weight in Google's ranking algorithm and no weight in Yahoo and Bing. Plus it's very likely that the change in domain ownership results in a dampening (decrease) in the value of the links pointing to that domain especially if Google sees a big change in the content. (Google became a registrar specifically to incorporate domain registration information into their ranking algorithm.)