Here is what I know about the subject. Vista was to be released this year and has since been moved back a number of times. By now, I believe that it is due some time in early 07. This is why Microsoft products are often called "vaporware.:
There has been no discussion of the price yet. There has been talks that it will start out at $99 for the Vista Stater Edition. But you can expect the Ultimate Edition to go for about $300-$400. Since they have already released the news of the Office 2007 proces which are a little more than Office 2003 prices you can bet the Vista will be more than XP.