You don't need 100M to make a good movie. You need 100M to make a movie that is trying to hide its own inadequacies by spending an insane amount of money on special effects and well-known actors.
That is not to say that there aren't movies that are worth spending 100M to make - but the market-driven talentless big budget movies that are coming out of Hollywood? We could well do without them.
That being said, most movies that have a 100M budget earn back their money in theatres, so I'm not convinced that with a downsized copyright system (no copyright whatsoever sounds silly, considering the term covers quite a few different bases, many of which are not impeded on by person-to-person sharing) they would run into big problems.