Gaijin Friendly Apartments in Chiba

Sakura House Apartments and Guest House
Sakura House is probably one of the most well-known names in guest houses for foreigners in Japan. They have a long history of dealing with foreigners so they are very understanding of foreigner needs. They offer cheap rates, clean rooms, they don't require key money, guarantor, or agent fees, all their rooms are furnished, they have a free internet line available in most rooms, rent including utilities is payable by major credit cards, and they have staff that can speak English, Chinese, Korean and French. They have quite a lot of rooms so you could probably find an opening. Check out their website for more information.

House Mate in Makuhari
I have heard from several foreigner friends that House Mate was very gaijin friendly and that they had good rates too.