One thing to note here is
Page rank and search engine rank(SERP) are totally different.
While Search engine ranking depends on lot of things, Pagerank depends only the rank of the website that links to you and number of website page links to.
Consider you get a link from page which is PR6 and total external links in that page is just yours. Then you get lot of link juice.
Doesn't matter if its paid or not.
Link swapping doesn't work because you pass link juice back to them. it will work if you have this setup
Web1(yours) link to web2(someone else)
Web2(Someone else) links to web3(yours)
Now web3 gains link juice.
One more thing to note is IP address of server that links to you.. make sure its all different and its not from *.wordpress.com/*.blogspot.com
If you want to increase your page rank
Get/buy permenant backlinks from pages which has >PR1
Page should have very less external links(Pref less than 10)
IP address of all websites that link to you should be unique.
Website should link to page where you are aiming to get high pagerank.
Getting high pagerank helps only in fame/link sales and has nothing to do with search engine ranking.