While not the fanciest enclosures, I highly recommend plastic rubbermaid containers. Small holes can be drilled in the lids for ventilation, they are stackable (since you will likely be getting more!) and easily cleaned. They can be purchased for under 6 dollars at any hardware store, and one manufacturer even has clear-view containers now, in which the front has great visibility. Most importantly, these containers are about as escape-proof as any you will find. Best wishes.