I dont think you have the space, but 10 of the hfi 12s will sound good, but... if you ever get on a meter youll be disappointed. ive done a few setups with them and they sounded great, got really low, but didnt meter high.
if your looking to save money i would just browse the forsale section for a while till something pops up that you like.
oh and if you get the hfi subs, right when you bet them, go ahead a break of the black plastic piece covering up the magnet. if you dont youll here a buzz when any bass around 65 to 70hz plays,