sound deadening is worth every cent.
if you are prepared to do it yourself $100 worth of sound deadening in your doors will make a massive difference to the sound quality. this relies on you pulling the door trims off and installing it yourself. it is unlikely to take longer than 2-3 hrs (so allow a whole afternoon just in case). i think most installers will charge about $250-$300 per door.....
bear in mind if you spend $100 extra on your deck, splits, sub, amp and cables i defy you to hear any difference.
i have sound deadened both doors and under the back seat and wheel arches, i used 2 sheets of serenity max, it weighs 4kg/m each sheet was 1.3x1m.
the biggest sound difference was the doors.
if you lived in Sydney i would help you do it.