I figure the magic price is $10/month for all-you-can-eat
Just remember that there are other issues besides price. There has to be a sufficient warehouse of music, the quality must be high (not likely to happen), and what we're able to do with that music is very important. If I am not able to do what I want with it, the service is useless.
A BIG incentive for me to pay for such a service is something that the record companies probably won't bother with: old and out of print material. If there's nothing but what's on TRL at the moment, you won't find me there.
But above all, I'm with Bitt. I want my CD.