How much will Mavericks cost?

I just ordered a macbook air haswell for school and totally forgot about mavericks, my macbook is literally scheduled to be delivered the 10th, same day as mavericks may be announced. So I will most likely still have to pay, so will it $20 like mountain lion, go back to $30 like the old versions of os x, or maybe they'll make it free since the changes aren't very big just minor additions.