Thanks everyone. I figured it could not be "free". Leverage is valuable, so a person selling the future should want to charge for it. Also, the person selling the future has to cover the risk that the greatly leveraged product increases (or decreases based on the future) hugely, which costs something (or they have to bear that increased risk themselves and should get compensated for it). So it all makes sense that they should have a cost.
When you hold a futures contract, you do not pay or receive money in the form of interest. So just ignore whatever lead you to that conclusion.
You would know this yourself if you have ever held a futures contract.
