i was in the same boat as you, same car, even similar amount of money.
this is what i did
got a pioneer double din head unit from ebay, $410 RRP $800
http://www.pioneer.com.au/products/car_ent...amp;broadband=1
speakers i just got randomly because they were marked down. i didnt intend to keep everything pioneer
6x9's $150 RRP $260
splits $250 RRP $350
installation at garys car radio was $70 for head deck and $230 for front and back speakers/tweeters custom spacers and whole car rewired.
next on the list is a 4 channel amp/amp kit/sub amp/install
as you can see shit gets out of hand very quickly. i would recommend getting a good head deck and a pair of splits installed, after that go for some 6 inches on the back parcel shelf and then 4 channel amp/sound deadening.
i had a go at installing this stuff myself but it was hard and not worth the effort, especialy having to take out the back seats for the 6x9's. sometimes its ALOT easier and less frustrating to just cut your losses and pay for something to get done right the first time.
for me sound quality isnt that important in my car. i just wanted a head deck that looked cool and something louder then stock. if i wanted superior harmonic bliss i would put on my sennheisers or crank up the jamo's at home.
edit: if you decide to get stuff installed at jb or strathies dont worry they arnt that bad, at least they come with a lifetime warranty no matter how badly they butcher your car.