Just my few cents - I bought a started package (here on BHW) of blog comments. It was only 10 PR1 and 5 PR2 comments.
After PR update my site got PR1 (Actually, 2 sites - same packages)
What im saying, if I chose a higher package with more backling and higher PR, I would get even more than PR1. So..all you gotta do is spend a few (literally, few) dollars and you're all set.
It also depend on your goals, mine was to check if comments can work for getting PR for my sites and as I said.. CHECK!