Need help with pricing an offer

I have an offer for Win desktops which monetizes by banner ad injection, in text links, shopping and new tab. Offer has about 80% success install rate. If I am buying installs from networks, what would be fair price at this time of the year (right before holiday shopping season) for US?

It should depend of live time value of injected user so you can tweak that PPI rate accordingly to ad revenues generated from that techniques. Think of moderate $0.50-0.70 USD per one US install on a good traffic.