I have a multi-function machine from boc. IT has a mig torch, tig torch and a arc torch. I have only used it on mig so far and it works well. Cost me a grand.
it will not tig alloy.
this unit will not allow adjustment of the wire speed, just the volts. some find this hard to use, but i dont know any better so its not an issue for me.
Paid a grand for it directly from BOC.
You will also need a helmet, gloves, clamps and magnets flap wheels and stuff. Leave about 3-350 to get started with this, and a 15a plug in teh wall. Check what the shed is wired with. IF you have 2.5tps tile it should then just buy a plug from bunnings and swap it over.
i have made gates and modded my sub frame. When i start my body repairs i will put out the tig and learn how to use that also.
there are other machines out there but i chose teh BOC unit as boc will keep spares for many years. Most of the units in the price bracket are made in china and i had concerns regarding parts long term.
Also look at bunnings for the coregas swap a bottle scheme. Cheaper than BOC. 190 deposit(refundable if you take it back) on the bottle and about 120 per bottle on a swap basis after that.