I guess if the premise or concept sounds interesting, they may fund a test pilot just to see if the series would be as interesting as it sounds... maybe? I don't know. I do know that in some cases, if the network is the one to offer a studio or company to do a show, they'll give them a budget to see what they can come up with; again, some guy at NBC was intrigued by Japanese singing duo Pink Lady (who were like The Beatles of Japan), and wanted Sid & Marty Krofft to do a variety show with them, since they had already had the likes of DONNY & MARIE and THE BRADY BUNCH VARIETY HOUR under their belt, so NBC gave them a million dollars to do a test tape to see what kind of a variety show could be built around the duo.
Of course, back then, there was a comfort and trust level that networks don't even have today: if you were able to get on their comfort level, and earn their trust, they would probably give you the money necessary to do whatever it is you want to do, but that wasn't always easy to do.
Of course, back then, there was a comfort and trust level that networks don't even have today: if you were able to get on their comfort level, and earn their trust, they would probably give you the money necessary to do whatever it is you want to do, but that wasn't always easy to do.