Exodus DPL-15's are $280 a pair plus shipping. I suggest an EP2500 amp for power, they can be found for under $300. You'll need a high pass filter at 16 hz to protect the subs from over excursion, the Reckhorn B1 can do the job for about $100. That puts you in the $700 ball park.
The advantage of the EP2500 is it has enough power for a second pair of subs should you decide you want more output in the future. There is enough volume in the 4' x 7' x7' room on the right side for a second pair. The Reckhorn can do both pairs.
Yellow is the output of one pair of DPL-15's You can expect 118 db at 20 hz, assuming 6 db of room gain.