I used a piece of suede leather I found at WalMart - $4.95 for an 8 1/2 x 11 sheet. I used a heavy duty snap kit that came with some punches to brad them to the material (Prym Sewing brand#14008) to keep them from falling out. I cut the leather to size then glued the pieces together with Duco Cement which is similar to contact cement but comes in a 1 oz tube. I put a bead of glue on the edge of both of the pieces and spread it flat with my finger then let it dry about 5 mins. Then put a second bead on one of the pieces, put them together and clamp them between a couple pieces of wood. Let dry about 1 hour before you use it. The snaps are really optional but you could actually use velcro and have a better looking case I think...
Here are some images of the case. (sorry bout the links...can't post pics for some reason. seems I can't turn HTML on.)
www.plasmicinjection.com/temp/pick_case1.jpg
www.plasmicinjection.com/temp/pick_case2.jpg
www.plasmicinjection.com/temp/pick_case3.jpg