Plastic mold injection

A few weeks ago I got a nice set of glass-lens sunglasses, and around the same time I got a new fanny-pack with a slot for my PDA. That means there's less room in the fanny pack for everything else. At the same time, the sunglasses being in a hard case means they can't dangle loose from the fanny pack and have to be inside it, which takes up even more room. So even having removed everything I can spare from the fanny pack, it's very tight.

I want to make sure those sunglasses last and don't get bent or crushed, so I need a firm case, not the soft one that came with it. But the only kind I can find so far is a clamshell-style case which is many times thicker than the sunglasses. It's big enough to fit sunglasses that don't fold very flat, but these fold so flat they could fit into an envelope.

I keep wishing I could find a very slender case. It wouldn't need to fold open; just a rigid-sided sleeve the right size would do perfectly fine. But it would have to be the right size. I can picture precisely what I need and if someone manufactured it would cost pennies to make, but I can't think where to buy it.

This is just the latest in a long string of times I've wished I had some way to create such things myself. A CAD system that could manufacture plastic items to my specifications, or simply a plastic mold injection system designed for consumers. Imagine how many handy things you could make that would just exactly fit what you need it for, but which aren't worth it for the manufacturers to make, inventory, distribute, price, and deal with.

I can't very well make it myself from wood, metal, cloth, or anything else I can work in because it wouldn't be rigid, or it wouldn't be lightweight, or it wouldn't be slim.

Wouldn't it be nice if someone could make a plastic mold injection system for home use? I bet I'd buy one.