The numbers I heard thrown about a lot were that Klugheim, as an entire project, cost €60 million (~£50 million / $67 million). For some extra context, I heard Chiapas cost €35-40 million, and RCDB lists Deep in Africa (but not including the hotel) as €22 million. Keep in mind inflation rates and stuff too (I think €22 million in 2006 is about €32 million these days?)
I'd fully expect Rookburgh to cost more than Klugheim due to the fact FLY is a bit more complex than Taron, the hotel is almost definitely a bigger investment than Raik and the significant amount of groundwork required in Rookburgh (which I believe is one of the things which has slowed the whole project down, due to it being more complex than originally expected).
Wasn't there some rumour that Taron was discounted too, due to the antics that happened with Chiapas?