my small room is also with in your dimensions, 1 door, 2 windows <900 ft^3,
I had 2 Klipsch sub 10's "smartly" located in the room
Then I ran REW and found my response at below 38 hz all but disappeared.
Short answer I built a THTLP 24" wide ,from Bill Fitzmaurice plans. using a BASH 300.
So have you considered DIY ?
for your budget you can get a really great ROI for varying degrees of effort
and some of the flat packs offered around here, just too easy to not say no, thank you.
keep us posted
THE BIG ROOM: Mitsy DLP 73837 Xbox1 PS3 slim Panny BD 220
Denon X4000 and Emotiva UPA7 for 9.2
Klipsch F3 FL/R, G-28 C, RB 51's, FW's , RS3II SBL/R, RC3II, SL/R, SLX-FH's
2 30" BF THTLP'S and SubMaximus and Inuke6000DSP