Trance bass doesn't dig that deep, so I would go for SPL and sound quality. This is one instance where deep bass porting isn't going to help. If it were me, I would go for either this kit
or this kit
. If the Klipsch RW-12d were on sale, I would say go for a pair of those, they might not be as sharp as those Dayton kits but the room mode smoothing is a bigger boost in overall sound quality than any overhang from ports that you would get from the Klipsch. As for the Dayton kits, those ought to hit pretty hard, they have very good drivers and a robust amp. The assembly itself is very easy, seriously, watch the video, all you need is a screwdriver, some glue, and a half hour. I think those subs would be a lot better than the sealed 12"s you can get from SVS and Emotiva for the same price, both of which show some pretty strict limited and will never hit any decent SPLs. The PSA XS15 ought to be pretty good too, although $115 over you max budget of $600.
Another direction you might look at is live sound subwoofers. These don't dig very deep but boy do they get loud. Some of them require separate amplification, but cheap amps can be bought off of ebay and the whole package will still be under $600. You can get something like this Behringer
which will make your ears give up before it does. That will have enough extension for most trance and also the monster SPLs you get at actual clubs. Get a separate amp and you can have this 18" beat from JBL
. That will make the kick drums feel like someone is actually kicking you in the chest. Here
is its more robust big brother for $500, if you are feeling really hardcore. Here is a self-powered Mackie for $700 if you want live sound 18" SPLs but don't feel like screwing around with a separate amp.