(Studies have shown that the sales-displacing effect of piracy in music ranges from 42% to no effect at all[1]. If all piracy could be prevented, that's an awfully large deadweight loss)
In this case $0 or even a negative value amount is what you can plug into something. Why? Think about artists that tried pay-what-you-want model. A lot of people pay $0. Some pay $0.10. But a lot pay $0.
However, what they pay with is with their time and attention.
I used to know someone who managed a movie theater. He would sneak us into movies quite often. Good and bad. And quite often after coming out of the movie I felt like wanting "my free back".
Let's say an artist is unknown and I am a customer that has quite a few connection ( a blog with a large following perhaps ). Then what would make sense is for me to pay a negative amount ( the artist would pay me to spend my time listening to his new cool record in the hopes that I might spread the news about it ).
FWIW, the only album I've paid for in years was a pay-what-you-want deal. I paid something like $3. Which was all that was left in my bank account after I paid my rent and bought groceries for that month - I'm a college student.
Do you have any evidence that the costs outweigh the benefits?
And without exception, all of those "pirates" that I know have much larger legal bluray and record collections than I do.