4 inchmid range with tweeters such as focal 100vrs or 100 krs $400 to $500, a pair of earthquake sws $400 or so, amp $350 to $500 dependin on brand, installation may be $300. Do this first, and if you still want more bass you can always add a subwoofer later. The earthquake are 8 inch woofers and 2 of them do produce decent amount of bass, although they don't play that low. Not familiar with shops in Melbourne, but any decent specialized car audio shop should be able to do it. The install is pretty straight forward.