Are fewer and far between than a few years ago when Google lowered PR accross the board.  Many sites that were PR7 or PR8 are not PR5 and PR6.
So the higher Pagerank pages that sell links are in very short supply raising prices, and the glut of lower pagerank sites lowers there price.
The good news for text link buyers is that you can now get a pagerank 4 link that has the streanth of a pagerank 7 link two years ago for pennies on the dollar - but you need to know what your looking for.
 

Are all about supply and demand.  Google changed the PR scale makeing high page rank sites more rare so of course the price would be higher.

Still, a quality text link is worth it's wieght in gold and garbage text links are still garbage.

Quality text links are always costly. But I don't think that low PR links rates are slashed. Every link has according to its qulaity.

But some people are selling high price in Pr1 sites too.