$1 US is about 1.14 AU so I'm just going to use US$..
The deck is not a priority if you have output in the back to connect to an amp. If you have decent factory speakers, those will work until you blow them
For a decent deck, you're looking at about $200.
Speakers are hard to say, it depends on how many and what size your car uses. You also need to keep the Wattage in mind. I'd say $200-$300 if you want speakers that last.
You could find an alright Bass package with box/subs/amp for anywhere between $150 -$300. Just don't buy shitty packages.
Go test products at car audio shops, and have them install it if you don't want to deal with it. Be careful though - they'll likely trick you into spending more if they live off commission. Do a little research and show them that you know a bit about what you're trying to buy. Don't let them fuck with the Woodster!