Ex Machina is fantastic and the closest thing to a Ghost in the Shell movie and only cost 15 million to make.
With a good writer and some District 9 level good FX I reckon an interesting ghost in the Shell movie could be made for like 30 million.
The weird thing about studios though is that they wouldnt be interested in making that movie. A large part of the appeal in adapting something like GitS is the never-ending chase for blockbusters and franchises. The studios are more focused on hitting home runs, often without giving enough attention to how much the strike out.
There's lots of anime they could make for a fraction of the budget of GitS. But to the studios, the question becomes why adapt that all if you aren't going to throw a ton of money at it. Easier to just buy the rights to an unproduced screenplay that isn't an adaptation and make that.
It's a self-fulfilling prophecy at this point.
There's some benefit to chasing blockbusters, but not to the degree it's done.