u do realise that to weld alloy and steel successfully with the one mig it involves having 2 different gas bottles and 2 different wires. if you wanna do alloy it has to be a gas mig. also alloy is very hard to learn to do.
Have a look at amweld.com.au, they have a oxy/acetelne torch system which they reckon can weld almost anything, got some specials going this month and they are in brisvegas too!!