Lucas gets a break in cost, because its done in-house by ILM. So, what would cost Michael Bay $30 million, probably only costs him $25 million. And the price will continue to fall as the years go on. But Lucas will spending much more time than Michael Bay would to convert them because he wants them done right, so the price will probably be back up to $30 million. But trust me, TPM will make a good amount of money. I would predict $70-110 million, but it could be more depending on how well they hype it. Also, its hard to factor in advertising costs--those are paid for, at least in part if not in full, by Twentieth Century Fox. So for Lucasfilm, its a pretty decent gravy train. It also might not be just about money--Lucas will be in his mid-70s by the time the OT is being released, and this might sort of be his last hurrah to enshrine his legacy and create a fun experience with the films that people will remember.

Also, this is a package deal. TPM will do decent business, because it is the first film and people will want to see Star Wars in 3D. AOTC will slump massively, though ROTS will pick up the pace probably close to TPM levels. But then ANH and ESB will skyrocket. ROTJ won't do as well, but likely better than the prequels. So it all evens out--if one film does a bit lesser like AOTC, it is more than made up for by ANH. What is important is the profits at the end of the day, when all six films are over and done with. In any package deal there are weak links that depend on the strong entries to balance out the profit.