Congratulations on completing your script. So few people finish, you should be proud! Make sure you register it with an internationally recognized body and good luck with the next step. Getting your work noticed by a producer with a track record can be tough. New writers inhabit a 'no-man's land' of needing a track record to get an agent; but not having a track record to attract an agent in order to submit to a producer. Yikes!
Agents for the most part work on commission; and they work darn hard, too I might add. And an agent who has been in the business long enough to be useful, has a vast network of connections that rival many producers or lawyers. They've spent years building their reputations and connections, not to mention the money it's taken. Often their return on any contract is a meager 10% to offset the effort it's taken to create this infrastructure and the daily expenses that go with it. It's not cheap to live in Hollywood; nor to employ people there either.
So, I ask you (just as they are probably asking themselves) - What's in it, for them? What can you give them in return for the vast amount of time and energy they've already put on the table by simply taking your call? The thrill an agent gets in making a really talented discovery probably won't pay many bills for years to come. What's an aspiring screenwriter to do?
First of all, polish the script that you have. Every scene needs to be solid as a house and ring with the truth of conviction. Second, start ANOTHER SCREENPLAY. No artist approaches a gallery for a show with ONE painting. In your writing portfolio you should have a variety of scripts that show the breadth of your talent; various genres, various characters and all bright as new pennies. And third, enter competitions. Do some of the agent's work for them... get your name out there!
But be smart about what you enter; you can spend a small fortune there are so many competitions now. Pick several that offer significant prizes (Final Draft, Disney) or recognition (Nicholls, or big Film Festival) or both. And then enter a number of smaller competitions too - where the odds aren't so tough. A win in Topeka still prints out FIRST PLACE on your script resume.
And finally, KEEP WRITING. Don't let yourself fall prey to discouragement! Keep writing and perfecting your craft; keep hoping and keep marketing yourself and your writing so one day an agent will pick up the phone with enthusiasm when you call.
I hope this helps. I wish you every luck with your screenplay and would love to read what's next!