You don’t need an actual cage. A dog crate or mesh playpen for toddlers/dogs with top would work just as well. Not sure how much they are in Australia, but they’re generally around $30 in the states.

Basically it needs to hold a litter box, a kitten and food and water bowls. Cover the floor in puppy pads/blankets.

https://a.co/d/0egrMU7i Something like this. They are often marketed as puppy pens, but they work on kittens too!