Know a fair bit about all this with the wife being a MFA Screenwriting grad from UCLA who has just joined the WGA and is working with Chicago Pacific on some of their projects
Hollywood is currently more risk-averse than ever before - unless you know someone who knows someone, or have a reputation from somewhere or somehow, are adapting a property, or are making a low-budget independent there is a miniscule chance of your script even being read let alone getting anywhere near production.
Payment-wise, 'big movies' are guided by WGA rates which depend on the exact nature of work being done and , anything from $5,000 a week to (IIRC) around $80,000 minimum for a 'big-budget' movie.
Some of my wife's professors favourite quotes:
"Ideas are like *&^-holes - everyone has one"
"So you have an idea, all that is left to write a script is everything"
That said - if you have a good enough idea to get into rough script form, you could probably pay a proper screenwriter a fee and they will put it in the proper format so it at least won't get thrown in the bin for being the equivalent of a CV written in Comic Sans.
If you want a great example of how to write a debut movie, watch The Disappearance of Alice Creed - 3 actors, one room, zero special FX but a razor-sharp script - a producer's dream.
Not to be all negative though, no-one ever gets anywhere in the movie business, unless you're one of the people that get a break