Spend a bit more and I will work out a really good price on one of these:
Shopping Secure - Car Audio Specialists - Steg QM 45.4x
Italian made amplifier, great build quality. Something you would want to keep in every car in the future.
That said you would be much better off getting this isntead:
VIBE - CBR12 Enclosure
Sub/Box/Amp/Wiring Kit for $699
It will sound better, get louder and I'm confident that it offers better value for money and build quality than what you are looking at now. That would be the best all in one package available to you for the money. Theres another package I can sell you for $599 that will still be better than what your looking at:
VIBE - Slick Pack 0.1 but to be honest I think the first package will sound twice as good for another $100.
Check out the review Philthy wrote on the double sub package:
http://forums.justcommodores.com.au/shopping-secure/117207-vibe-cbr12-review.html
If your on a budget I think this is the best way for you to do it. It might seem like a little bit more than the others but when you consider your getting EVERYTHING required for bass in your system and your also getting a wiring kit then this package really starts to shine when it comes to value for money. The sub is valued at $400, your looking at amplifiers for $280, a good quality box will cost $200 for an installer to fabricate for you. Your talking about more than $900 worth of value packed into $699. I honestly think that one of these would be the best option if your on a budget.