Subwoofer Suggestion

Hi guys I need your suggestion regarding subwoofers. My system is composed of Focal Kanta 3, Kanta center, 706BK it would be used 50/50 for music and HT. My room size would be 13m by 4m by 3(Length,width,height). Would it be better to go for dual pb1000/sb1000 or single sb3000 or single pb2000 or single PSA S1500?
king baracyda I'm located in Philippines, everything here is so expensive compared to US.
Thanks ieales I'll check the prices of martin logan subs here thank you.

El Pipe-O is a DIY sub. Quite a large variety of woofers can be used as drivers. I’m sure you could find a suitable pair locally. 
Well I'm not really looking for a diy sub, but if all else fails I'll give it a try thank you.
I bought 2 SVS sb2000 subs on sale for $650 each (price reduced when they brought out the sb2000 pro model).  They compliment my Martin Logan 60XT towers.  I set the crossover at 80HZ and let the subs handle frequencies below that.  Room placement is not optimized and I seldom play music real loud.   I’m not sure I have them dialed in correctly — read somewhere that mains show be set at 20 HZ and let the subs handle below that (?).  Don’t know if that advice works or not.