Gander: my room is 4.4 x 5m and it has 15 foot ceings. With regards to size of sub i want the smallest one i can get away with to be honest.As far as I'm concerned, there are no subs that will effectively fill that size room at the sort of size you're looking for. The Sunfire's True EQ Signature is going to be a little over your budget......
It will depend on how much sub bass you're after. If you want to 'pressurize' the room (meaning actually shifting air in the room, making it a truly physical experience), you will have to look at larger subs. The above mentioned sub gets surprisingly low for it's diminutive size, but isn't going to give you the sort of effect of someone slamming a snug fitting door (hope you know what I mean there!). Our dem room is a little smaller than yours, and it takes something an M&K MX250 or 350 to do that. Other subs can do the bass, but not shift it round the room in the same way.
If you only need to hear the bass, there's the Sunfire HRS8 or HRS12, Monitor Audio RSW12, Dynaudio SUB250 or SUB300, or if looks are important, you could even use two KEF HTB2SE's.........
It's all down to the performance you want from it. If you're serious, you're going to have to sacrifice a little bit of space.