brewers den in boronia will do a keg king 6kg cylinder for $350 with a $50 dollar exchange.
Ive just been through the process of buying a keg set up. I watched evilbay for a couple of months and found kegs and associated gear in melbourne went for as much or more than you can get it retail once you factor in collecting the stuff and buying seal kits etc. you might fluke it for an ebay bargain, but in two months I didnt see anything go for a price that made it worth leaving the house.
The best deal on kegs from my research is a draw between mybeershop.com.au. and craft brewer. Both $60 ber keg. mybeershop kegs are cleaned, re-sealed and pressure tested but you pay for postage, arround $20. Craftbrewer will post 4 kegs for free with seal kits included, but you have to clean the kegs yourself and they havent been tested. I went with craftbrewer. kegs needed the seal kits and one needs a new gas post but that what you expect for second hand kegs, theyve been used and knocked about.
The best deal i could find for gas was the 2.6kg keg king bottle off ebay. $160 plus $20 postage. swap and go exchange at the brewers den.
I cant comment on regs. I bought a micromatic on the basis of buy the quality and buy it once. gas line, couplings etc are all much of a muchness unless you want to inport as has been mentioned. Craftbrewer looked after me on local pricing of all parts once i spoke to them about ordering a system.
I bought one of the plastic bronco taps because my funds were limited and they were recomended to me. its not impressive to look at, but for getting beer from your keg into a glass im quite happy with the performance and the $60+ thats still in my pocket from not buying the stainless pluto gun.