Basically i'm not fussy at all, 700$ is my maximum (prefer to spend a bit less even) but aside from that i dont mind, as long as its loud and easy to find in a fairly local store. however i do like the idea of two 12" subs, whatever brand. but thats just a thought and i can easily change my mind if you have a better idea, especially if its one 12" that is as loud as the 2 sony xplods... (i kind of need the boot space)
Go in to your Local shops that sell audio like, JB HI FI, Autobarn, Supercheap Auto, strathfield car radio etc. and just start doing some research on what subs and ampps you can get to fit your budget, that would be a start than come back on here and name the list of subs you like and let people on here say what they think would be the better choice