I remember when I was booking my holiday to Australia, I found it very exasperating that these packages seemed to be so prohibitively expensive. The cost was high whether I booked an inclusive package through a tour operator or even reserved each part of the holiday package separately.
Then I found that I was very annoyed by the fact that the tour operators that travel to Australia, seem to have an agreement whereby they refuse to publish the cost of the whole package in advance - they would only give you the cost of the flipping hotels and one idea of a fare that you will not find available when you try to go ahead and book - very unhelpful. In the end, I realised that I did not like the way in which these companies were being so disingenuous and decided to avoid them altogether.
I found the best way to tackle the extraordinary Australia was to definitely take care of arrangements myself. I booked a flight that included several Qantas and BA flights together and this was on a special round-the-world fare that meant that I just had to keep travelling east around the globe. This actually worked out as being excellent value for money, although I would encourage you to steer clear of Qantas for your flights - I thought they were horrendous! - and try to stick to BA.
This only leaves your accommodation arrangements, which again, can be secured independently. If a large party are intending to travel to Australia, it is definitely wise to think about booking self catering rental properties - these will save you beaucoup bucks over the hotels. If hotels are your only choice, try to aim for a property that is away from the main tourist draws and this could save you too.