I take directly from http://www.backlinks.com/kb/index.php/article/how-much-do-i-earn-for-each-text-link-sold as follows:

How much do I earn for each text link sold?

You will be paid the following monthly rates for text links sold on your web page(s). Rates are paid per month per text link.

PageRank (PR) 1 homepage $.50 , subpage $.50
PageRank (PR) 2 homepage $1 , subpage $1
PageRank (PR) 3 homepage $2 , subpage $1.50
PageRank (PR) 4 homepage $3 , subpage $2
PageRank (PR) 5 homepage $4.50 , subpage $3.50
PageRank (PR) 6 homepage $12.50 , subpage $10
PageRank (PR) 7 homepage $30 , subpage $25
PageRank (PR) 8 homepage $75 , subpage $50

I hope it answers your question. Thanks.