Those are some pretty brutal space restrictions, not to mention budget restrictions for a room of that size. The most ideal sub for that space would be the Elemental Designs P7-650 , although it is an inch over your space restrictions, but the problem is it is twice your budget. Next to that I would just get three A3s-250 subs and stack 'em, you could do that for under $1k, although it might be pretty weak bass for a room like that. I'm sorry to say it, but it looks like your in a kobayashi Maru scenario as far as getting any kind of decent bass in there.