If you want to write a movie, write a book

"I’m not sure when it happened exactly, but it seems a lot of aspiring screenwriters out there are playing by the rules … or at least what writers of screenwriting books call “the rules.”

I’m talking about aspiring screenwriters who worry about the budget. While I think there’s definitely places for screenwriters to guide production teams from the page, budget simply isn’t one of them. You can curve around camera direction, blocking, lighting, sound, and pretty much anything else, including budget, but budget is the only thing you simply shouldn’t focus on. Not only is it not a screenwriter’s job, it’s completely opposite of what creative people are good at: numbers. If you’re a right-brain oriented creative, then chances are you’re probably best when you’re allowing your imagination to stream through your song, dance, acting, painting, or writing."

http://www.scriptxray.com/2009/02/27/screenwriters-if-you-want-to-write-a-movie-write-a-book/