maybe i'm wrong. but a link form a pr0 indexed page is still a link. PR is just a google thing, while links helps with all other search engines. About insane charging from some directories: I do not buy links, so they can charge whatever they want ehehe!
All links are not created equal! While PR is not an important measuring stick for how your own site is doing, it does mean a lot when searching for inbound links. The higher the PR of the page linking to you the more Google will value the link... 100 links from a PR0 or PR 1 page does not equal what one link from a PR7 or PR8 page can bring. Granted there are other things to consider like quantity of links on the linking page etc... but this is the rule in a nut shell.