I have an open source project website where users download the product, integrate it into their web site and then there is a powered by backlink on their site to my projects site. This is the reason of the high PR. The site has the following stats:
17'700 Indexed Pages
~60'000 Alexa
~ 1800 Daily visitors

More and more advertisers are coming to ask for backlinks. So my question is how much would you charge for a site like this for a site wide backlink? I'm new on selling backlinks so I need some expert opinion on this not make prices too low or high?