People who want something that they don't think they can afford always wish it was cheaper, or free. Be that a guitar, a song, or a nice car. However, I sort of think that if you're given something for free, then generally it has no value to you.
Those who have spent their money (or their time which is often of more value) for something, can assign what they feel that money or time represents to the value of the "something." Sometimes you might even feel like you've gotten a "deal" and gained more then your money or time was worth to you.
Neither of these is an absolute truth. You can be given something for free that has a very strong emotional value and you can pay for something that turns out to be worthless. But I think for the majority of transactions, what you are willing to pay for something represents it's minimum value to you.
This certainly isn't limited to music. If you're handy with a computer, try helping someone fix theirs and see how much value they assign to your time the next time they lose a printer button, or get a virus, or whatnot.
Here's a good example about music. I'm sure we all know at least 1 someone who filled up their computer with music during the heyday of Napster. Now they have Gigabytes of music, most of which they may not have even listened to in the last few years. Those of us who purchased our music did so because we made an emotional connection to the music, or the lyrics. We may not have gigabytes of songs on our hard drives or I-Pods, but every song, or artist on there can can invoke an emotional response. So our smaller music collection has more value because we were willing to pay for it.