I have to admit I have a weakness in this area. Whenever anyone asks for money or investors, I get less than nice about how I help. I find this is the one area where "tough love" is necessary.
If you go to real production companies and real investors and not know what Return on Investment is, nonetheless having already registered with the Securities and Exchange Commission (SEC) - you have no prayer of getting your movie made or getting a dime.
Imagine the horrible first impression that would make on a potential investor. You can't undo that (CNTRL-Z). It's actually great advice (not an opinion) to say you are not ready to make a movie with a $500,000 budget, plus I too believe that this is some random number that is not based on a breakdown of the script. Being asked these questions here on the forum and NOT with people who might make you an offer DID help - you're learning something, albeit you took it harshly.
Now, please understand this is a learning process. No one is insulting you or putting you down. We're just assessing where you are at in your development as a filmmaker. You have the same respect as everyone else.
When asked what credits you had as a writer and director, you merely said you were the writer/director. What credits do you have? Have you ever written anything produced that people can see? Similarly what can people see from what you have directed? Has anything you've directed made a profit? If so, how much was the budget and what was the ROI?
The point is that $500,000 is half a million dollars. If nothing you've written or directed has made anyone any money, the risk on this investment will go up exponentially. Have you seen a lot of people's first movies? They are not that good, and generally don't make any money. There's no evidence that you (meaning any first time filmmaker) will create something great if they haven't made anything before.
Take yourself out of the situation and look at it from the investors' standpoint or the production company. The metaphor is asking for half a million dollars to hold a series of concerts for a guitar player who has never sold a ticket, nonetheless picked up a guitar before (if you haven't made any movies before).