Who should bear the cost? The person who believes in it.
And if you're an untested writer, that means you'll need to demonstrate the power of your idea by creating a compelling screenplay (or hiring someone to do it for you).
We strongly encourage you to take your ideas to fruition, and we're always looking for quality material. But do it right! Craft a screenplay the producer can believe in. Until you do, your idea doesn't help a company like ours.