This question is a never ending story, and finally found it’s way into the FAQ

Presell Pages are not about PR (pagerank). Search engine optimization is not about PR (pagerank).

The value of a presell page is estimated by factors like age, trust (expressed in .edu/.gov links, traffic, search engine rankings, .etc) and finally the topic.

That means the inventory prices are pretty static, and in any case NOT related to the pagerank of the site… you don’t want your links on an unrelated PR6 site if you find a well related PR4 !

Publisher-Q: but my site changed its PR from 5 to 6 in the last update – I want more money for the presell page

A: sorry, we don’t change prices with PR updates – neither up nor down

Advertiser-Q: the site hosting our page went down in the last PR update… please adjust prices accordingly

A: sorry, we don’t change prices with PR updates – neither up nor down