Nick be very careful with cheap subs. There are a lot of cheap subs out there that are aimed at the Home Theater market, which has much looser SQ requirements than we have for music. In a HT system the sub pretty much is used to provide impact. It doesn't need to be of the highest quality as long as it gets you attention. For example, when you are just reproducing the dinosaur thumps as the T-Tex is chasing someone in Jurassic Park or explosions during the attack scenes in Pearl Harbor sound quality can be secondary to the visceral effect. As long as the bass shakes the floor and hits you in the chest it will do just fine (for the most part.) Many of these subs to just fine when watching movies, but fall far short when used to reproduce music. In sound effects the impact of the boom is the primary objective. However in a high end audio situation we want much more. When listening to tympani drums in and orchestral piece pure impact is not enough we also wand to hear speed and articulation in that we should distinctly be able to hear the impact of the drum hit separate from the resonance of the drum itself and be able to track the rise and fall time of the sound. When listening to something like a Ray Brown bass solo we want the resolution to hear all of the individual note stand on there own instead of being mushy and just running into one another.
The bottom line here is that cheap bass is easy, but rarely very good and good bass is hard to do and in most case hard equates to $$$.
IMO opinion while stereo subs is always a desirable situation, you would be much better off with a single high quality sub as opposed to a pair of cheap ones.
Also keep in mind that subs are strange creatures and there optimal placement rarely coincides with what out other halves would consider pleasing from a decorating point of view. So if you don't have a dedicated room where you would have the freedom to place the subs anywhere they need to be, you might just be better off having one and keep the disagreements to a minimum. As someone who move from a house with a dedicated listening space that was all mine to do what I wanted with to a house where the only place to put the system is in the Living Room I am dealing with this kind of issue all the time not only with subs, but also with speaker placement in general, acoustic treatments etc. I deal with this kind of thing all the time.
I ended up getting a pair of Carver True Subwoofer Super Jrs which are small and I can tuck them somewhat out of sight. I know there are places in the room that they would sound better, but...........
I actually started out getting one, but a few months after I got the first one a second one popped up on eBay for a stupidly cheap price so I couldn't not give it a try.
Had it not been for that I would have been OK with one.