You can figure out the cost in a jiffy but you might not know to factor in mass production effects. There are those that will ask this but not get that last effect right.
Your comment about MP3 is odd. I don't have that issue nor anyone else I know. We put our collection on hard disks and it's good for many years. We also have backups so when a hard disk fails (rare!) we don't lose a thing.
Does anyone know what the size limits are with memory cards. Is it possible to make 100gb cards with the technology at it's present level? What size is the largest available at the moment? I am thinking of MP3 files that can only be stored on HDs (which are not fully reliable) for the bigger memory sizes.