OK, I have actualy dabbled in all three of the stated examples below, so I have a slight insight into them all.
Just my two cents, but I'd say (and this comes from reading around) it's probably hardest to sell a screenplay (imagine the huge $$$ you're asking someone to invest in you, the crew/cast/equipment expenses ... it's murder & miracles if it gets made) ...
Well, depends what you're talking about. There are lots of people looking to get in movies. It's a sexy investment even WITH the risks. So selling a movie script isn't always as hard as you might think. Getting that movie made is where it gets difficult. And that's where the money starts to really burn.
Next, imagine the difficulty of selling a comix sctipt WITHOUT having Art attached ... because others nailed it for you above: ART is the thing that sells the comix. Consider the small market you're selling to; you think there are lotsa titles? But it's a tiny market of people who'll publish and distribute something they cannot even visualize WITHOUT seeing the Art!.
Again, this is not as difficult as you might think. Once you are in the loop, as a writer you CAN pitch a project and you can sell that idea. WITHOUT an art team. BUT, if you are breaking in, you NEED the art as well. Editors can read a script and visualize it. They wouldn't be doing the job if they couldn't. They simply don't have time to trawl through a slush-pile. And because the industry is so much smaller, they can't afford to hire readers in the same way that movie producers and agents can and do.
The issue is, the more people and $$$ needed the greater the inertia to get the ball rolling.
This is true. I can write a script (just costs my time and the cost of printing a copy and electric to run the computer) I can get an talented artist who is trying to break in to do the art on a percentage of the back-end, same with an inker, colorist and letterer. I can then pitch a finished book to an indie publisher who ONLY needs to cover printing and some marketing (which in reality Diamond will do the heavy lifting on to the book stores). I'm not gonna make a lot of money, but I will have a bok out there and real published credit.
I cannot get a director, actors, lighting, sound, catering, transport, sets (even if I use existing places there are costs involved), editing, prints made, marketing and distribution with everyone taking a back-end pay.
BUT, I can sell the option on a movie script and leave the making of to someone else. Not only wouldn't I sell the option on a comic, to break-in, I would need to do a chunk of the "producers" work either.
Movies need an ARMY to become involved, a rich Army. Or all you got is words-on-paper.
Yes, but that's not your problem. You just sell the script. The movie making is not your problem.
Comix need Artists and marketing, or all you got is words-on-paper.
See I would say this is why it is a litle hard, because to break in YOU need to find the people to make it more than words-on-paper.
Writing NOVELS though? You need nobody but ... you. You and a dull pencil and a hill of blank paper ... and the visions in your head that could be a movie or a comix or ... a novel!
Prose is the ultimate no-$$$-investment, just your talent getting it rolling. And the world is FULL of people hungry to publish a book! (But even then it's feast-or-famine)
Actually no. You can do it all yourself for the same costs as above, but if the book is published it needs a lot behind it to succeed.
I'd say: start with short fiction, get some buzz going, start writing novels ... and join the fray! If the novels sell well ... the movie deals and comix adaptations will knock on your door.
There is a world of difference between the way you write those different things. And I have seen it said many times that the worst person, in most cases, to adapt a novel is the author.
The reason comics are hard to crack is because there is an "old boys club" vibe. I have heard it said LOTS of times, that you should never ask anyone how they broke in, because the industry immediately closed off that way in. It's hard to break into comics because the industry makes it hard.