To the best of my knowledge, there is only one pet store cage on the market that meets the minimum, and it's the Midwest Guinea Pig Habitat. I've never actually seen it in a store, though, everybody I know that has one has ordered it online.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry