Don't buy back-links.......... just try to get some back-links from natural link building techniques.
Pr is all abotu backlinks yes, any backlink from any low PR site passes on a bit of PR. Links from higher PR sites generally pass on more PR than small ones of course. The ideal case is getting link places near the top on high PR sites with low amount of outgoing dofollow links. I hope this makes it clear enough
By using standard links,up to mark key words are the tricks that are used more often to increase the page rank.Another good thing to consider is to write a quality article.
the only way to improve your PR is building dofollow backlink, the PR is depends on the PR juice and only dofollow backlink is providing the PR juice
try to build natural backlinks with certain variations.. for example... dont create 500 backlinks within an hour... variations of backlinks such as web 2.0, forum profiles, article submissions, high pr links, non pr links, dofollow, nofollow links, wiki links, every day try new variations .....and be consistant while building links......dont rush to get more links within short time.....
Keep original and informative content on your site. Internal link structuring it should be well site structure. You can get pr soon
You need more high quality back links from high PR websites. Note that having high PR doesn't mean that you will automatically rank well.