GA Russell - Probably around $15 since I'd have to go pick up extra colors in the same yarn. $10 if I already had the necessary colors on hand. I lucked out with these since my store had all three colors in their clearance bin.
silverraven - Love your cover, too! I have been planning to look for a dollar store album cover that I could modify in a similar way, but I keep forgetting to stop by the store. Have you tried decoupage before? I have some Discworld calendar pages from previous years that I'd love to put on a hard back cover for my JBL.
Ken - If you finished the edge of the sock and hemmed it before it could begin fraying, I think that would work just fine. It wouldn't be too tough to work up a pattern for a sewn pouch in something like twill with a softer inner lining either. Good idea with the patch. I have a couple of unit patches from my 4 years in the Army that would look pretty swanky on an olive drab and black version of my sleeve.
Yayafava - This is technically a sleeve for my netbook, but I made it out of Lily Sugar and Cream cotton in Lime Stripes using a shell stitch. It would be cute in a smaller size for the JBL, too, I think.