Sony makes nice TVs. They make terrible car audio equipment.
The reality is that if you can get all of that equipment for $200, none of it is good quality. Unfortunately, car audio is a department where you get exactly what you pay for. The "master unit" in that kit puts out 17 watts RMS; that's probably half or less of what the factory head unit does.
Your factory system sounds better than that kit would.
If you just want a sub for some bass, you can usually pull that off with $300 if you install it yourself. If you want a sub and new speakers and amps for everything, you'll have to spend more dollars.
MODS: PW TMIC, Cobb catted DP, HKS cat-back, AVO filter, Bren e-tune; Konis/Epics, Advan RCII