its roughly $50 per end so $200ish + allignment so it sounds about right. you can do it yourself if its just coilovers, I did and just pay for the alignment. doing the whole bush thing is another story as some of them need a pressing machine and a bit of labour hence the cost. you will need camber kits at least if your going lower than stock ride.
A good shop will look over your car and tell you if you need to replace them or not. most of the time you dont need to.
have a look at sydney kids suspension group buy. might save you a couple bucks