Cheapest way to get to Australia from Indonesia

OK, so in the last part of my gap year I'm planning on island hopping across Indonesia from the tip of the malaysian peninsula to SE indonesia, and then going over to Australia. Whats the cheapest way to get there? Where is the most south-eastern indonesian airport? Also, is it possible to catch a ferry across to Darwin?

There is no ferry between either Indonesia or PNG and anywhere in Australia.
Probably the cheapest fares Indonesia to Australia would be tourist specials out of Bali.

I've found the best way now... You can fly from Dilli (East Timor) to Darwin :D