There is no way to answer this. That's like saying how much is a site worth if it's 50mb, 500mb. 5gb, or 50gb. It's just a parameter. PR gets factored in very often but only because it's a quick assessment of backlinks and how much google likes the site. Current because of the 4/4 update Pagerank has some problems. Google seemed to hand out PR5+ to many new pages and sites. Example...
http://www.sitefight.com/contact_us.php and it's a PR6...!!!! No ryhme no reason which now most webmasters have completely lost confidence in PR as a parameter. It's possible the algo has changed or there is a bug in the ranking system. Either way webmasters and domainers need to adjust.