Indeed. Even if there was such a contract, who fixed the price for it? In other words: who said that the right price/service in exchange for an incredibly precise audit trail of my behavior is targeted ads or some pretty lame free articles?

I paid my Navigon app, I pay for my Office 365 e-mail, I pay for the music I get, I pay for the local newspaper I read, I pay to access academia papers (i.e. ACM), I pay for a lot of tools many of which on a donor contract.

I don't even have a problem to pay a fee for a social site if I believe it gives me value in exchange.

Let's forge the contract in a different way: you want my data, you offer something in exchange, I decide if that's a good deal for me. If not, I may still decide to give you my data, but you pay.