Quite a while back I found those CD sleeves for A4 folders in my local discounter.
There were 5 of those sleeves, holding 4 CDs each. First thing I needed to do was cut them in half.
Then I put some colorful adhesive tape on the sleeve, right where I wanted to punch the holes.
I folded it over and taped the backside as well. Almost done already! The only thing I still had to do was punch. I use a one hole punch, so I had to use an original Filofax insert as a stencil and punch through the tape and sleeve. I found that doing it like ripping of a band-aid (fast!!) was easiest. And now - TADAA:
My CD sleeves hold 2 CDs each plus either a list with tracks on the CD or whatever else you want to insert into the small pocket on each side (I chose to store little stickers in there, see above). I spent about 3€ on the sleeves and half an hour working on them. I now have 10 sleeves for my A5, holding 2 CDs each, which would have cost me nearly 100€ had I bought the original ones. Granted, mine probably won't survive decades, but still, I am very happy with them!