Have you considered hiring a local carpenter to build you a wooden cage or DIY-ing one yourself? Wood's pretty cheap, fairly light, and basically plastic if you put enough coats of epoxy over it. A pro carpenter should be able to build an enclosure to whatever dimensions you'd like. It may wind up being the most cost-efficient option, especially if you'd like some larger cages.

I'd imagine a cage as long as narrow as a 72x24x24 needs some sort of center brace, regardless of material and whether you want to stack on top of it or not.