Diane Duane considers POD
However, as this article from BoingBoing points out, Warner has decided not to publish the third book in a trilogy she was writing (among other books) because sales of the first two lagged. Her potential solution? POD that bad boy--since fans as been asking her to finish the series.
From her blog:
The obvious solution to this problem is publication on demand (POD). I don't mind doing that. But you have to understand that it ain't cheap at the reader's end. Without dragging you all through the math -- which would take me a while, and I have enough trouble with math after the caffeine hits, let alone before it -- let's just say that a "trade paperback" perfect-bound copy of The Big Meow is going to cost you hardcover prices, not paperback. If I'm to make any money at all on the deal (by which I mean, at least recoup my publishing and labor expenses), you're going to be paying $20-25 for a copy of this book.
The truth is, however, that TO VISIT THE QUEEN is published by Warner/Aspect and is selling for $18.99 (for 354 pages.) I'm not sure POD would be any higher, really.