Movies aren't expensive to make, unless you want to make them expensive. The technology involved has been getting cheaper year after year. Take "monsters" for example. It's a sci-fi movie in the best tradition, that doesn't look low-budget, and that cost less than a million dollars to make.
I think the problem is that studio's have too many incentives to increase budgets and few reasons to trim them. I'm sure they could make the same movies they make today for a fifth of the budget, if they reorganized themselves around doing that.
Movies are very expensive to market (average cost in Hollywood is over $20 million in marketing), and a movie _without_ marketing -- virtually regardless of the how much it cost to make -- will do almost no theatrical business at all.
Tarsem's "The Fall" is a great example: the guy spent tens of millions of dollars of his own money making a pretty interesting film, had no marketing, and did just a few million at the box office, despite moviegoers liking the film.
I think the problem is that studio's have too many incentives to increase budgets and few reasons to trim them. I'm sure they could make the same movies they make today for a fifth of the budget, if they reorganized themselves around doing that.