Ikea have a Lack table that some people have used to make cages with - it's melamine. They do a 90cm one (about 30 inches). If you get two you can use the two table tops as the top and bottom and the legs as the corner struts. Basically it's a table on top of another table so it's a cage on legs
I assume the sides would be mesh or plexi. Or you could just use one table upside down and make a top lid out of wood and mesh and perspex the sides.
As with anything, check for chewing, but I think they'd find it hard to chew through melamine.
You don't need the middle shelf, but could use it as a solid back maybe. It's a fairly cheap option but plexi can make it more expensive I think. Because the pieces are the right size and the edges finished in melamine you haven't got the chewing risk of just having melamine cut to size and raw edges.
LACK Coffee table White 90x55 cm - IKEA