I have a few sites that the pagerank has gone up on, 2 are PR3 now, but I'd like to know what value is put on different PR's. I know PR1 is less valuable than PR2, is less valuable than PR3 etc. but is there a minimum value that a website could or would sell for depending on it's pagerank? I.E a PR1 site would be worth $x and PR2 worth $xx and so on....

Is there a guideline published anywhere? Or a rule of thumb? I've searched and been unable to find an answer anywhere. I may sell some sites soon so it'd be handy to know what I could ask for as a starting price and expect as a final price (or at least have some idea).