A friend of mine is a happy customer of Nuts.com. Their products are really good, and their boxes are sooo cool. One day, I was looking at a small Nuts.com box, and I realized that it was a near-perfect fit for my GC, so I grabbed some tape, a knife, and some scissors and got to work. I'd say no more than thirty minutes went by, and I had a decent looking and quite functional case. As of right now, there is a metal clip closing the electrical connection on the lid sensor, but that will soon be replaced with some sort of switch. The tubular thing sticking out of the top functions as the power switch. I've tried Googling "cardboard GameCube case", etc., but to no avail, so I think I may have created the internet's first cardboard GameCube case mod. Well, I'm sure there have probably been others out there, but this is the only one that I know of. I hope this gives any financially challenged modders out there some ideas.
-Joshua Martin