Mig/Tig/Stick welding Q's....help...

[botboy]

Alright, I'll start by saying I'm learning about welding, but I think I've come to the limit I can do with my current setup, and I'm looking at upgrading.

My current setups are as follows:
My dad has always had a 30-250 Amp stick welder that works well. Old, but functions well, and since I'm at home when I'm not at school, thats what I use for stick welding functions. Welder runs on 220 single phase and has a 70% duty cycle

I also have a lincoln weld-pak 100 (originally used w/flux core wire) that I've personally upgraded to mig with a 60 Cubic foot bottle, regulator and flow meter (along with some mig wire instead of the flux core). This welder has a whopping 4 voltage settings and variable wire speed. Welder runs on 120 with a pathetic duty cycle.

I think I've come to the limits of what the weld-pak will do, and am looking to upgrade. I like the idea of going tig, but at the cost of used miller econotigs hovering around $1500, the cost is prohibitive.

Now my understanding is that a stick welder would also be what is considered a "power source" for either a mig wire feeder or a tig "inverter"...is this correct? Does this explain why most tig welders are also setup to do stick with an extra set of cables?

If this assumption is correct, can I purchase a tig "inverter", torch, and foot pedal, attach it to my dads stick welder as a power source, attach it to my bottle/reg/flow meter and weld with it? Or is it more complicated than that?

Also, does anyone have any recommendations for inverters? Aside from staying with a major brand such as hobart, miller, or lincoln? Specific models?

My spending limit right now is something around $500, minus whatever I can get by selling the weld-pak.

For application, I generally weld stuff under 1/4", just light fab work, fixing trailers and farm impliments with mig. If I have to weld heavier stuff I do it with the stick welder. I'm also looking to be doing more bodywork, I've done some bodywork with the weld-pak after I converted it to mig but generally the settings are either too hot or too cold and don't do much but either burn thru or not lay a very good weld, thus the need for an upgrade.

Its also my understanding that I could do more with aluminum with a tig than with a standard mig, but that I could weld aluminum with a special mig gun (one that has the spool on the gun itself) and a different argon blend. With tig, would I need a different argon blend to weld aluminum also? Its my understanding that the gun stays the same, is that correct?