Great Sub for NHT Classic Threes?

Hello, I've got a nifty bedroom system consisting of a Creek 5350 SE Integrated and a new pair of NHT Classic Threes that I'm just crazy about. I'd like to add a subwoofer to the system but don't know much about subs or how to hook them into a system. Any suggestions would be deeply appreciated. I'd like to keep the total cost of a sub and required cables under $1000 if that's possible? The room is 10 x 18 feet.

Add about $250 and I'd recommend the Velodyne DD-12 which you can find on AG used and in good shape and/or with very little use.
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does not nht make a sub? as they are going out of biz i bet u could steal one. i hope that you have a big enough room to really get anything out of a sub. 18 ft. is fine but 10 ft might get boomy. u put a sub in there and u best treat the corners acoustically. they sound like they are nice spkrs from reviews i read.
Good suggestion the NHT S-20 might be a good choice.