Very good question.
Since I have been in the business for over twenty years, I think I could probably answer your question with a bit more accuracy here.
First and foremost, get it out of your head that your potential agent will do all the legwork for you, and put everything together for you. This is NOT their job whatsoever. Your relationship with an agent/manager/producer, etc., is a WORKING relationship. Meaning if you are not bringing anything to the table for your agent, s/he will not bring anything to the table for you. It is on you to network and develop contacts that will help you get your foot in the door. It is on you to KEEP WRITING. If you have the one story, but leave it at that, your agent will forget about you as easily as he forgot about the socks he got for Christmas last year. It is on you to pitch to production companies, NOT your agent. An agent's clientele can be upwards of 20, so if one of them expects her/him to do all the work, he is going to quickly cut that client from his list.
If you are lucky enough to sign with an agency, you can expect your agent to set up meetings with production companies for you. But if you walk through that door, time after time, and continue to bomb and not bring anything to the table, your agent will cut you, because the last thing he will do is keep around a client that gives him a bad name.
I think you get the point by now, so I will move on.
Your expenses to get your material read can be pretty pricey, depending on how resourceful you are. Of course, if ANY agent, manager, producer asks for a price just to read your material, they are not legitimate. There is a man out there, one of the few, named Eddie Kritzer that snags people via craigslist and asks for a $600.00 certified money order just to read your material. It's a scam, and he is not the only one. Plus, it is against WGA regulations.
Most boutique agencies and production companies prefer to receive query letters and submissions via email. Obviously, this is a huge help to the writer. However, MOST DO NOT. So you can expect to send THOUSANDS of query letters via snail mail, and of the few requests for your material that you will receive, you will be spending additional monies on shipping your script. If you live in the LA area, visit scriptcopier.com, a site and business that helps the working screenwriter save a bit. You can always call, but be ready with a polished logline and pitch because that phone could go "click" before you utter a word. The Hollywood Creative Directory and Representation Directory are the ideal sources for numbers, addresses, and emails.
Now lets say you do not live in LA, and you get some HUGE interest in your script from an agent/manager/producer, and they want to meet you. GREAT! This is fantastic news of course! But you get to foot EVERY travel expense that it takes to get out there, and get home of course. Unless you are about to get signed by one of the "Big Five" (technically four now since William Morris and Endeavor merged) agencies, or a HUGE MONSTER production company, no one is going to foot the bill to meet a screenwriter with no credits, and no name. This is why if you are serious about breaking in, you may as well start saving money now to live in the LA area. Most agents/managers/prodcos do not pay any attention to you if you live outside of the industry. They need you accessible in order to make money. It's the simple out of sight, out of mind philosophy.
Ok, so your script is bought, and now it's time to pay the ones who made it happen. Per Writers Guild Association (WGA) standards and requirements, agents do not take more than 10%. Managers same, but if you have an entertainment attorney involved, you can expect they may take a 15% cut of your hard earned money. So let's say you got really lucky and sold the script for $100,000. Well, $35,000 of that already has a staked claim. In addition, you would be wise to PAY YOUR TAXES on the check immediately, because tax evasion is something NO WRITER SHOULD EVEN CONSIDER, because you will NOT get away with it. This is basically another $10,000 you can send off to Uncle Sam. What is more, is that you will get paid in increments (usually) just as if you had won the lottery (which technically, you did). So when you make that big sale, keep in mind you aren't an all star and super rich quite yet.
Now if you are truly planning on financing your film on your own (become a producer) then you will spend as much as you are willing to make the movie good. And a "cheap" movie in Hollywood usually doesn't cost less than a mil to make when all is said and done. So I would recommend that if you want producer credit on your films, wait until your second film, when you have the money to qualify.
All in all, this is a dream that few are successful at. The ones that survive the THOUSANDS of obstacles that this town presents, are rewarded greatly in the end. The ones that do not, were not meant to be here in the first place.
You HAVE TO HAVE THE TALENT
You HAVE TO HAVE THE PASSION
You HAVE TO HAVE THE PLAN
Good luck to you, and I wish your endeavors well.
check em out