Well, there is nothing special for SERPs about the pagerank. I think PR4 website could easily rank out the PR7. Speaking about money, normally, PR7 sells for $50-$100+/month depending on many factors: sitewide/homepage, pages indexed, content, etc ... So, I think that permanent link would sell for $500+ I am not sure though ...
I think it also depends greatly on how many outgoing links there are on the PR7 page. If there are hundreds of outgoing links, you will get very low PR value, if any, from that webpage. You would be better off getting a link on a related PR4 page with low outgoing links.
thx for your information , yes it also depends greatly on how many outgoing links there are on the PR7 page. If there are hundreds of outgoing links, you will get very low PR value
As discussed by many here, it depends upon the OBL and popularity of the site. If your site has strong PR7 with good amount of quality backlinks. One would be happy to pay you $100/ month for a quality PR7 Link.
I don't think there is any value of high PR websites in SERP. It is good to get links on old sites with unique content.
Do not give too much importance for PR7. There are many other important parameters such as the number of outgoing links, the site theme, and the most important in case of permanent link: PR7 is not forever - after 3-4 months it may be equal to 1 or even 0...
High pagerank linkback is always appreciate from google in my opinion. You must consider the position of the link better if in the same niche blog, and with lots of text around the link, like in a post/article. I think link in blogroll are not very valued from google.
I totally agree with Mzonas. I know some PR two and three sites over take High PR sites in the SERP. It's a different thing. We can't exactly predict the relation between PR and SERP.