I'm not sure about lightweight, as all the stuff in the cages can make even a light one heavy, but what about a front-opening cage that doesn't need to be moved to clean it? There's the
Nightangel cage, as meganm suggested, but
Bucatstate also does a cage that's, erm, 'inspired' by the Nightangel stacker cages for around 30% less, plus it's has a bigger option (linked). These are heavy cages by themselves, though, being metal.
Otherwise, the only thing I can really think of is the ZooZone2, which is a 'tank' plastic cage that opens from the top. The ZZ2 has very large bars at the top, but I've been using mine for years with my robos and have never had an escape (because it's too high; would probably need to mesh it if I added levels). There's a similar style that has smaller bars, but I can't remember the name/brand.