'For the theatre, I write something that fascinates me and I shop it around. In television, you're told what to write and then you hope it becomes fascinating.'-- Nicky Silver
-- Janet Blake
If money is your primary motivation for being a playwright, don't do it. The only reason to be any kind of creative writer is because you're compelled to put words on paper. Nothing else will give you enough motivation to write that 90-page minimum required for a full-length play.
You can make a living at this if you're good. And lucky. Needing both talent and luck may seem a bit unfair, but that's always been the artist's lot. As a playwright, you need both to rack up enough productions by Regional Theatres and commercial producers, and film adaptations of your plays to give you whatever you think is enough.
Despite the potential royalties from productions, the sorry fact is that the majority of produced playwrights need a day job to make it work. That's life in America for all kinds of artists: only a small percentage in any field make enough from their art to support themselves.
That's why Television series work is such a seductive lure for playwrights. Lotus Land has lots of jobs for you once you've gotten some recognition from major Competitions or productions.
But here's something to think
Putting words on paper is an odd business, no matter how or where you do it. And taking a day job that has you doing this, whether it's in journalism, television, advertising, or technical writing, may satisfy your compulsion to write to such an extent that you'll never feel up to starting that next play.
http://www.vcu.edu/arts/playwriting/