Giving your situation, Arsenals would probably be better, considering they are a SQ sub, but they aren't quiet either (Xluben has some vids of his two 12"s with some nice flexing going on //content.invisioncic.com/y282845/emoticons/naughty.gif.94359f346c0f1259df8038d60b41863e.gif). I just suggested the Arsenals, I'm sure someone else will have an opinion on something else, but what I posted above would sound great and get loud.
About your box though, don't buy one. Build one. Buying a sealed box is ok, but generally, if you set your stuff up right, you get better low-end with a ported box, and chances are good you won't find a good ported box tuned exactly how you wanted in your price range (you'd have to get it custom built from someone on the forums or a local shop). In other words, it'd be best for you to build your own ported box.