Individuals are unlikely to make much money by selling their own data, yet the same data in the aggregate can be worth a lot. Gregory Barber, from Wired, who recently tried to put his facebook data on the market, managed to make a grand total of 0.3 cents.
The economics here are a bit like the economics of voting. If it were legal, and you tried to sell your vote and your vote alone, you might not get much more than 0.3 cents. That vote is unlikely to prove decisive. Yet average and marginal value do not coincide. If someone could buy a whole block of votes, which in turn could swing an election, the price could be much higher.