Hi kes88,
I have done Melbourne - Antananarivo (TNR) about six times over the last couple of years. It is not the easiest itinerary on earth. Now your situation might be a bit different to mine, as I get the impression that you are touring there and really want to minimise cost. In my case they were business trips and convenience was as important as cost. Here's how I went:
MEL - SYD on Qantas.
SYD - JNB on Qantas. (Only flies 5 days per week)
JNB - TNR on South African
Then the reverse coming home. This itinerary was always frustrating because the need to pass through both SYD and JNB added many miles onto the journey. And what is especially frustrating is that the flight path from SYD to JNB passes right over the top of MEL.
On one occasion I went MEL - PER on QF, then PER - JNB on SA. But from memory I think that was more expensive and just as time consuming.
Now here's an alternative which may suit you better. I'm not quite up to date on it, but it was possible to fly Melbourne to Mauritius (MRU) direct on Air Mauritius, and there are also direct connections between Mauritius and Antananarivo on either Air Madagascar and Air Mauritius. So that's a fairly direct one-stop trip which looks attractive on the face of it. For me the trouble was that the MEL - MRU leg was never available on the day I wanted it, and a layover in Mauritius was always necessary. But you might see this as a plus.
If you don't mind me asking, why do you want to go to Antananarivo? (Yes, it's a tongue twister. Everyone calls it Tana for short). I just proposed it on another thread as one of the least attractive destinations on earth. Maybe I was being a bit harsh. It is not without a few points of interest, and there are a few surprisingly good French restaurants there (up on the hill near the parliament building). But, gee, there's a lot of filth and the pollution is terrible.
Madagascar has some fabulous beaches, but getting to them is quite a challenge. The state of the roads is appalling.
English is virtually no use to you there, but if you know French you will be fine. The local currency is the ariary, and there's about ten million of them to the dollar! (Exagerating again). The local people are very poor, but I found them to be delightful. Take anti-malaria pills and carry a good first-aid kit. Basic services, including medical facilities, are poor.
Good luck
Cocitus 23.