Head units are always good to decent at worst.
I woul look into other subs, speakers and amplifiers.
Cadence has a summer sale going on for Amplifiers, really good prices for power!
Subs... Well theres many to choose from. The one you are looking at is very low end.
If you could afford a bit more power, theres a guy on my board selling Elevation Audio SQX subs for very cheap... Hes also got amps for cheap, check it out
www.caraudiocentral.net