The PR does not mean a whole lot, and it depends on the site. You wouldnt say $100 for a PR 1, because some PR 1's are worth more than $100 and some are worth way way less.
Pr is often given more importance than they deserve . As said above its not good to determine domain with it.
Well i didn't renewed a PR3 site and expired. I would not pay more than 10 $ for a PR 3 domain ( if the domain is good, has traffic and it's brandable ).