First of all, for hour building, you don't need to go to one of the big schools. As you already have a license (ok, you'll need the US based-on one to fly in the US, but that's no big hassle
AFAIK), you can rent an a/c from anywhere. That said, I'd look beyond the usual suspects.
Secondly, it depends, what you are trying to achieve. If you are only after logbook hours, then probably somewhere in the Midwest might be a good and cheap idea. If you want to learn something and gain experience in a wide variety of environments (both in terms of airspace and topography), then I'd say go to California. Not as cheap as the center of the country, but great place to fly!
Just to give you two more in the LA area, try Justice Aviation (Santa Monica) and Channel Islands Aviation (Canarillo). There are loads and loads of others, though, you shouldn't have a problem finding one that works for you.
I would try to seek out some of the smaller FTOs, as the availability will in general be better than in the big 'sausage factory' outfits.
Enjoy!