Right now universal doesn't need anything new with all the additions coming in the next 2 years, so if Disney wanted them to tear down a land in one of their parks it's gonna cost Disney a lot more since universal needs some extra incentive to do so. But 5 or 6 years from now when the hype for potter is starting to settle down and universal raked in their mountains of money from it they will probably look at a way to boost attendance by doing a major refurbishment (seeing as Marvel is getting more popular that's probably want they'd try to refurb, and disney might not let that happen) they will then decide what and where do we do a re themeing and what do we retheme it to. That's when disney can step in and Uni gets paid to do something they were wanting to do. Super hero island is probably the easiest land to refurb at ioa, it's flat, there's no water rides you have to mess with, not to mention its a very large land area, and if you desired you could push it further into toon lagoon.Why would the price get cheaper? The only way it gets cheaper is if the Marvel properties stop making money at the box office and people stop buying merchandise in droves. The more it makes Disney, the more valuable the property and theme park rights become. Universal can set any price they want as they have all the advantage in terms of rights on the East Coast.
And I don't see how 1 billion isn't reasonable. Yes Universal can get more per dollar than Disney. But there is no incentive for Universal to say "we are only going to ask for exactly what we think the cost of a retheme would be." They can ask for the farm... Because they can. And if Disney really wants it, they are just going to have to eat the cost.
Right now it may cost disney 1 billion, but years from now if they are already looking at spending a large sum of money at the resort, 100 or 200 million might be enough to give them extra incentive