Depend on the quality of link The price is higher if you mean at the home page or subpage which itself have PR6 The price is much lower if the link is stay at the inner page (which is not PR6)of the PR6 site
Then, gotta look for the OBL, if this is a directory with tons of OBL, then it will be less than $100/yr If the website have less than 25OBL, it can sell at $100+per month
I wouldn't even pay 100 bucks for pr6 links on a page with a lot of outbound links-- google just looks at those as spam. Be careful buying links if you're not already knowledgeable in SEO-- there are a lot of worthless link building services out there.