What are your listening habits,,, bass expectations,,(are you chasing the deepest extension,,,, or the highest SPL that say a 16Hz ported sub would provide?) How many seating positions? Are you on a concrete slab or floating floor? At only 1230^3 you have the luxury of getting loads of bass SPL within your budget.
If on concrete i'd lean towards ported,,,, while a floating floor in just 1230^3 (sealed?) room would certainly do a pair of 15" sealed subs justice. If priority is just one or two seating positions, then a larger single sub could do very well. Any of the sub choices mentioned already will crush that small room with proper set up.
-Funk 21.0LX Master/Slave combo 4800 watts RMS/9600watts (peak)-
-Chane A-2.4 L/C/R
-Chane A-1.4 side/rear surrounds.