Maybe this will help you, now or later, : http://www.panalysis.com/resources/customer-acquisition-cost...

Sorry, wouldn't pay a dime. This is a little akin to buying 1000 twitter followers. Sure they'll give you apparent social proof, but you'll have a hard time selling to them. What you are really asking is how much is an unqualified lead worth. You can buy random traffic all day, but if none of them purchase/upgrade its worthless to you.

You have to ask yourself if you really think that you can convert any of these users. There is a world of difference between targeted and untargeted traffic. You probably wouldn't even get any usable metrics out of the deal.

You are also talking about an investment of 2 bucks per user, and you could almost do better with a basic cpc campaign. You'd end up spending a bit more, but you be much more targeted.