Going from how the old OS upgrade was priced, I would assume the usual $30 for an upgrade DVD. Considering that an OS install is fairly large and time consuming, I would imagine it to be for sale retail only. So far I don't think anyone has ever tried marketing an OS upgrade through online sales alone, it would just limit the customer base too much. As said earlier, regrettably there still exist internet providers that have rather tight data caps per month and an OS upgrade I would imagine to be in the 4-7gig range.
p.s. How do you like your new macbook? I remember you were unsure if you should return it and buy the refresh after the new model was released about 3 weeks after you bought yours.