Anyways, each Golgo 13 figure has had the M16 rifle stored in a case. I opted to replicate the Hot Toys version since it best fit the layout for the M16A2. Skynet's version is smaller, but I didn't like how the inside was arranged.
Figure 1: Hot Toys' case (top), Skynet's case (bottom)
I like my cases laid out orderly, with none of this "diagonal part orientation" business.
There's no point posting the sketches I used to build this case, since they're useless and indecipherable to you; not to mention you're totally not going to build this out of Magic: the Gathering cards.
To make the walls, I did the same technique as I did with the guitar. I laminated strips around the case backs and taped them down as the glue dried. Since there's a lip where the two case halves meet (it's there to help hold the case together when closed), I made the interior wall 2 cards thick and 1mm off from the remaining 2 outer layers. This gave me a 12mm interior wall height and a 13mm outer wall height for the lower case, and a 10mm inner/9mm outer for the top. After these dried, I glued them to the case backs. I added another sheet to the case backs to overlap the wall edges to help hold the two sides together and to hide the edges.
Added costs to the "Golgo 13 for Under $130" project: ~$3 (Matte Black paint and foam sheet)
Total costs so far: $66 (body) + $2 sculpey III head + $3 (XM-177 rifle) + $3 (paint and foam) = $74