With your budget I'd personally go with:
2 12": https://ssl.perfora.net/www.ficaraudio.com/...view.shopscript
Enough power for those subs and a great price: http://cgi.ebay.com/NEW-HIFONICS-BXi-2010D...mplifiers?hash=
0 Gauge amp kit: http://www.knukonceptz.com/productDetail.cfm?prodID=KFX-PK0
RCA cables: http://www.knukonceptz.com/productDetail.c...rodID=KARSS2.6M
Speaker cable. I'd get 12-15 ft: http://www.knukonceptz.com/productDetail.cfm?prodID=KAR10SS
Head Unit. 6 volt preouts, usb and aux ports, 20x4 watt rms for $130: http://onlinecarstereo.com/CarAudio/p_2085...rion_CZ309.aspx
For that system your looking at ~$940, you could build your own enclosure for $35 if you have the tools. Use 3/4" MDF board. Anyways, that's my input, hope it helped.
Oh and I just remembered, if you can find a good price on them, 2 12" funky pup subs will get louder than anything mentioned in this thread. Be careful.