If you've exhausted every potential investor and still can seem to come up with the money you need, and if you don't mind being forever referred to as "the filmmaker who got his/her break from a car company," check out The Chrysler Film Project. Your movie could be just what they're looking for.
If you can pull it together by April 20, all they need is an already produced short film (I'm assuming so they know you can actually make a film) and the finished screenplay you're itching to turn into a movie. There are, of course, a few caveats to consider before pinning your dreams to this chance.
First off, the script has to be able to be made for less than a million dollars. Sure, to you and me that sounds easy enough, but in Hollywood, that's chump change. Retool things if you'd planned on asking Reese Witherspoon to be your lead.
Second, if you're chosen as one of the five finalists out of the gajillion submissions, you'll be asked to make a three-minute, Chrysler-centric film. The final decision will be made on the quality of that film, so if you're cool with making a commercial in order to prove you're the next Scorsese, this might be the chance you're looking for.
Check out the website for more details, and if you're the one to get the deal, I expect a walk-on.