I used to be big into car stereos, have put various things into various cars with different budgets, MTX, JBL, RF Kicker subs, Phoenix gold, Alpine, Macaudio amps, and more different speakers than i can remember and I agree entirely with what has already been said.
The setup of any system is the key to getting it to sound good. But with that said the inside of a car is a terrbile place to try and reproduce good quality music. To even get close to anything that you'd consider awe inspiring on the SQ front you're going to need sound deadening all round, upgraded front speakers, new cabling, a GOOD (and by that read expensive) amp, a sub box built specifically for your car and musical tastes - a sub that also falls into that catagory, a top end head unit, and probably an EQ.
The maximum i think I've spent on any one install was somewhere topping £2500, and even then I wasn't entirely happy with what was coming out..... it's not an easy task.
So getting back on topic, my mk2 has got upgraded but factory sized speakers up front and in the back. They were however not expensive (JBLs in the back, and vibes in the front) TBH they don't sound a great deal better than the originals in a car with no sound deadening, a stainless exhaust and K&N..... they are running straight off a nakamichi head unit (which admittedly is nice, but again, wouldn't be that much different from any 70 quid sony xplode in actual audio quality), and in the boot is a 12" FLI active sub which I bought from Halfrauds this morning for £120.
It's an all in one unit, comes complete with all the wiring, sealed enclosure so the sound remains tight for rock/pop/classical type stuff, but in fairness did pretty well with a random R&B CD I chucked in to test it.
For the money it's a cracking unit, and if you do only want to spend £150, then I don't think you would be going far wrong. If you kept the gain set fairly low, but the crossover up a fair way, turned your bass down on the HU so you could put that little bit more volume through your standars, then if you're not a music producer, or audiophile I think you'll be happy enough.
