[A Quiet Boom]

I've got a Lincoln Tig Welder and all the accessories, think we paid $2300 for the welder alone. Anything over 3/8" is really pushing the duty cycle on my machine. It's enough of a pain that I'm on the lookout for a used 3-phase industrial sized tig and a spool gun. It's far cheaper to pay a pro to do the welds for you. If you're lucky you'll find a guy that will work with you and tell you what prep work should be done etc. I've done welding of AL, SS and steel for several local Pelicans AL requires a lot of amperage due to it's thermal transfer ability and besides that it takes more skill than most metals. Even if you do find a larger used tig in good shape you'll still need 100 or more amps to power it which far exceeds the power in an average home garage and in fact many older homes only have 100 amps total. You can run a 3 phase welder from single phase if you build or buy a rotary phase converter but it'll be a big one to supply a larger welder. Also tigs work best if you're sitting down at a bench to weld, trying to do bodywork and the like with one requires some pretty solid skills. I'd recommend a good Lincoln, Hobart or Miller mig 220V mig welder for most things and farm out your AL work.

EDIT: one more thing, don't even bother buying a tig for AL unless you plan to get a watercooled torch and cooler
(another $500 or so) without it the torch will burn you through the gloves trying to weld AL.