A Miller Econo tig is as low on the scale as I'd go.
Argon for all the steels.
Helieum or argon for aluminum.

If you're stick welder has AC ya can get a HF unit and use that for aluminum or the steels.
If the welder has DC straight polarity ya can just buy the torch and lead and do what they call a drag start but, can't do aluminum with it with out the HF exciter.
Weldcraft is an excelent tig torch $60.00 for one with a gas valve built into it, 200 amp.

Hope this helps,
BB1