re: New Subwoofer - Onkyo tx-nr676

Living Room space around 600 sqft (20w x 30d). Long Rectangle.
Kitchen and Sitting Room on either side. About 300 sqft each.
Kitchen (14w x 20d) is connected with an open concept and long side of both rooms runs parallel, but has a beam separating the ceilings.
Sitting room (20w x 14d) has some partitions for walls/ceiling and is only about half the depth of the living room. Short side sitting touches long side of living. So, some sound leaks in there, but not a lot... especially compared to kitchen.

_____xxxxxxxxx
xxxxxI_______I
I____I_______I
I____________I
I____________Ixxxxxxxx
I____________I_______I
I___________________I
I____________I_______I
IxxxxIxxxxxxxxxIxxxxxxxxI

*Not to exact proportions, but you get the idea.

I'd like to keep it under $1k. I've seen some $2.5-4k subs and think that's crazy.
I don't mind being in the $300-750 range if there is a good quality to value ratio. And I don't mind spending $1k if it's really worth it, but I'm not going to throw money at it just for fun.
I'm not that big of an audiophile.

I'm not really interested in DIY.