Jeff Hause, the writer of the original script (it was subsequently heavily rewritten) remembered how it got done:
"In 1984, I was in college, studying to become either an illustrator, sculptor, or animator -- I couldn't decide which. While sitting around in my dorm room doing nothing but avoiding the dreaded decision of my ultimate career choice, I wrote a screenplay for $2000 (that's TWO thousand -- not twenty thousand, not two hundred thousand) with my old friend Dave Hines for a producer who will remain nameless (not by me -- but by his reputation and track record).
It was called "Nightlife", and was about a teenager who gets bitten by a female vampire in Hollywood.
From this tiny seed, even tinier seeds would eventually grow."
You can read more of his memories on this page