What's it worth to you?
I've used the example of enjoying a book for four hours to be equivalent to enjoying Avatar (insert your own movie here) for four hours. That is, when you buy a book or movie, you're paying for enjoyment and entertainment, not medium. 
I mentioned this at Millenicon recently, and got the comment that Avatar took hundreds of millions of dollars to make, and a book doesn't.
And that's the strange concept. It doesn't make any difference. The amount of money (or time or effort) used to create something has NO inherent relationship to its cost.
Cost is all about how much I (or you, or anyone else) is willing to pay for something. Period. Reducing supply increases demand simply because there is no relationship between production cost and value to the purchaser.
Here's a simple analogy - and one I've seen before as a teacher: When some students do poorly on an assignment, they'll say "But I worked so hard on it!" That's really immaterial; it didn't meet the needs of the assignment.
Likewise, how much is spent on the medium of entertainment (both in dollars and time) is immaterial when meeting my entertainment needs. What matters is what that experience is worth to me.
There are other market forces working on the price of entertainment, but the cost to consumer - at least, what the consumer will buy - should have not have a primary relationship to how much it cost to produce something.  The obvious corollary here is that I'd love to see more dynamic pricing for "expensive" media like films. I don't know how that could effectively work, but there are definitely films I would have gladly paid twice ticket price... and then there's those where I felt ripped off by a matinée ticket.
 I'll put in the caveat that movies and live theater and books and audiobooks are not perfect substitutes here, and that not all examples within a category provide the same quality of entertainment, even though most paperbacks cost the same and most movies cost the same.
 At the same time, it can have a secondary relationship - "Wow, that was cool and must have taken forever/cost a lot to do. I'll give them more money!" I've noticed, though, that this only becomes invoked when the media is already appreciated and valued well.