Which subwoofer for £300 ish!!

Hi all, happy new year. 

Im looking for a subwoofer to partner kit in my sig, I have parted with the Wharfedale SW150 and after something better. 

Movies is my priority say... 75% & 25% music, room is 16' long x11' wide, sofa against back wall viewing down the 16' length, concrete carpeted floors. 

Ideally I'm looking to spend £300 ish, whether it be new or 2nd hand I don't mind, I would like a driver size of 12" and cabinet no larger than 15" cubed, depth not too much of an issue tbh. 

2nd hand could be a Rel Q400e, BK XXLS400, these generally go for £300 ish, These are both sealed cabinets but should still hit pretty low.

are there anymore you guys could recommend I look at, finish is not important as a vinyl wrap can be done professionally.

thanks all

Darrell