What he said. 
 
Unless you want to drop a bundle on an AC TIG setup or slightly less on a MIG and spool gun, drop Aluminium from your list.  Both MIG and TIG require gas which as noted costs several hundred extra to get into.  
Price wise, a half decent MMA setup (Stick) welder allow $300 to $500 - there are MUCH cheaper ones, but generally a few hundred dollars gets you a nice little inverter unit that is light and easy to use.
If you had a bit more coin to drop, then a MIG setup with bottle of MIG mix allow around $1000
Cheapest AC TIGS go for around $800 but I wouldn't touch one of these myself - next step up is around $1300 but even these aren't the best so you can see how quickly this gets expensive.  $2000 buys a nice unit, $4000+ buys a bloody brilliant one.  Again, add the $400 for a gas bottle - Aluminium uses straight argon, so you cant use the bottle you bought for your MIG either - bit of a bugger eh... 
 
Personally since getting my TIG, I use that the most and I love it, but a quick job will see me drag out the MIG.  I do have an older cheaper stick welder I take in the ute if I need to do something for someone - the good machines stay at home.
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