What Kind of Good is Public Radio?

My local public radio station is doing its pledge drive. I'm a shameless free-rider, but since I average only about 5 minutes a day of public radio, I figure it's ok to be without shame.

This morning, the announcer said that their listernship is growing, and that each new listener increases their costs. Now I'm puzzling over that. It seems to me that public radio is a toll good--that each new listener would have minimal, if any, effects on cost. (Unless you got those new listeners by putting up a new antenna to reach a new set of potential listeners).

So did NPR lie to me to get my money? Or is there something I'm missing?