As others have pointed out, getting down to 25 Hz and keeping things quiet for next door neighbors is a contradiction in terms. The wavelengths for notes that low are such that they easily travel through walls and interact in unpredictable ways both within your room and as they pass through walls into adjoining areas. A bass note that sounds normal from your listening position could actually sound louder and unbearably boomy next door. That's just the way that room acoustics work. In my house, I use a parametric equalizer to eliminate the room induced peaks at my listening position, but that doesn't stop the bass from sounding much boomier in the kitchen.

As far as which model to go with, there are plenty of very small subwoofers (cubes less than 12") that can still belt out notes that go way deep. REL, Velodyne, and Sunfire among others make tiny subwoofers that can go past 25 Hz. But, these models are very expensive (the Velodynes and Sunfires I believe start around $1,500), and therein lies the rub. In order to get that kind of extension from a small cabinet size, they rely on drivers with very long throws and require very powerful amps to get that decent output. Components that meet those requirements aren't cheap. It's easier to go with a larger cabinet and driver. It will give you the same extension, not require as powerful an amp, and cost less, but you got that large cabinet to deal with.

If you want a "tighter" sounding sub, then you'll probably want to go with a sealed sub because of their generally quicker transient response. Their advantages are that tighter sound, and more extended lows. Their disadvantages are that they are less efficient, the bass begins to drop off sooner than with a ported sub (but declines slower), and they can have higher distortion as the driver excursion increases in the lower frequencies. Those smaller high output subs that I mentioned are all sealed designs. If you're looking for something less expensive, then your range of options is very limited since your price point appears to be around $500. I have one of Adire's $400 Rava subs, which is a 12" sealed sub that has serviceable output well below 25 Hz. However, it is 18" on the outside, which might be too big for what you're looking for.

One option that seems to fit all of your requirements is the $600 Rocket UFW-10. It is a sealed 10" sub with an exterior dimension of 13" and available in a gloss rosewood or maple finish. From what I've read, it has decent extension (not quite as deep as the SVS, Hsu, or Adire options, but still very good) and it looks good.

http://www.av123.com/products_produc...rs&product=1.1

If you're looking at DIY options and looks are a priority, then I suggest that you contact some other sources as well. Acoustic Visions is one of Adire's major resellers and they offer a wide variety of finishes with their cabinets. Of course, the cost escalates once you opt for fancy veneers and better looking finishes.

http://www.acoustic-visions.com/~aco...painting.shtml

And as for why Hsu subs have ugly finishes. The answer is simple -- the majority of people who opt for one of their lower level subs would rather save a few extra bucks than pay more for a fancier finish. The Hsus have a great reputation for how they sound, and for around $350, their performance is what people are looking for. If you want the option for a better looking cabinet, then their $800 VTF-3 model is available in a piano black finish or rosewood veneer. Of course, that will cost you extra.