The primary driver in the value of PageRank is often driven by the fact that many people think they NEED high PageRank, but most industries are not dominated by PageRank. It is usually more effective to build a broad and cheap linking campaign vice buying exceptionally expensive high PageRank links.

There are a ton of locations where you can find cheap or free links and PageRank. One of my buddies has a PR6 site based on forum sig links. Just playing on the web for a while gives you PageRank you can use to manipulate any other industry. Since PageRank is so easy to manipulate Google can't make it a huge part of their relevancy algorithm, thus PageRank a True Commodity.